LinkedIn’s founder Reid Hoffman will be joining Greylock Partners as a partner but will continue to hold the role as executive chairman of LinkedIn. Hoffman tells us that he will be shifting his angel investing under Greylock Partners, where he will be a partner.

Greylock has also closed Greylock XIII, a $575 million fund, which will be used to invest in and support promising enterprise and consumer software, services and infrastructure ventures. Hoffman said that Greylock was the right fit because of the relationships he had with the partners, and the angel investing presence of the VC firm. Hoffman said that Greylock and his interests in funding early stage companies were aligned. He adds that he will continue to work full-time for LinkedIn.

LinkedIn has hit 50 million users, according to a blog post today, growing from 45 million users two months ago. And according to the latest comScore data, LinkedIn is steadily growing in terms of unique visitors. For September, LinkedIn had 9 million unique visitors in the U.S. compared to 8.7 million unique visitors in August. But it appears that LinkedIn’s growth is mainly attributed to a burgeoning international user base. Worldwide, LinkedIn grew from 18 million unique visitors in July to 20 million unique visitors in August.

The network’s CEO, Jeff Weiner, said in the post that half of LinkedIn’s membership is international, with 11 million users in Europe and 3 million users in India, which is seeing the fastest rate of adoption of LinkedIn. Weiner added that it took just 12 days for the network to accumulate the latest million users.

Here’s the thing I love about Reid Hoffman. There’s no “We-don’t-comment-on-rumors-and-speculation” BS with him. You ask him a question and he gives you an answer.

So you don’t need a bunch of words from me, just go to the jump and watch our final backstage interview of the conference where Hoffman talks about whether LinkedIn will buy Xing and whether it’ll file to go public this year.

Also, Hoffman names the three other tech companies he thinks can price pretty much whenever they want. (And lucky him, he’s an investor in two.)

While Facebook continues to grow, and some companies are getting more comfortable with using it for things like Pages, LinkedIn still fills the gap for users who want a more professional setting for social networking. A new service launching in public beta today at TechCrunch50, Radiusly, wants to take the idea of Twitter and put it in more of a professional setting, as well.

But unlike Facebook and LinkedIn which exist as two totally separate networks, Radiusly wants to integrate its service with Twitter. Users will be able to publish an update they leave on Radiusly to Twitter (and Facebook, as well). But the key selling-point is that in the Radiusly environment you can also do much more, such as have a professional profile, resume, sample works, and photos.

LinkedIn tonight celebrated their 45 millionth user sign up, according to LinkedIn’s Marketing Project Manager Florina Xhabija’s Twitter message.

According to comScore, LinkedIn had 16 million worldwide monthly unique visitors and 331 million page views in June 2009, up from 7.7 million and 114 million a year ago, respectively.

The company was valued at around $1 billion in its last (2008) round of financing, and says they’ve been profitable for 2+ years.

The Wall Street Journal has long envied the success of professional social network LinkedIn and its 15 million or so monthly visitors (WSJ.com has just a third of that). In late 2008 they launched WSJ Community, a social network bolted onto the main WSJ site. That community is a ghost town – raise your hand if you’ve even heard of it, let alone visited it. At some point, they’ll likely shut it down as quietly as possible.

But they are still serious about gunning for the LinkedIn crowd and all those monetization opportunities (jobs, ads and a heck of a marketing pool for WSJ subscriptions). They’ve been working on a new social network, to be called WSJ Connect, we’ve confirmed. And instead of building it internally, like they did with WSJ Community, they’ve enlisted the help of another arm of parent company News Corp. – Slingshot Labs. And yes, they call it “LinkedIn Killer” internally.

Slingshot Labs is the R&D arm of News Corp. and works on digital products. Their first product was Daily Fill, which launched earlier this year. They also built the MySpace Events product that we covered in March. They operate fairly independently, have their own funding and 40-50 staff, according to one person familiar with their operations.

WSJ Connect is still in the planning/conceptual stages, says one source, but there is “strong interest” to move the project forward. Importantly, it would leverage the WSJ brand but would be a separate property and unencumbered by the need for a paid subscription to the newspaper.

There is an IBM commercial that pokes fun of people who spend time on social networks in the workplace. It shows a young, hip guy who brags about having “826 friends” and explains to an older boss-lady type that he “can find anyone.” So she says she needs a team of international finance experts who know merger arbitrage, speak Cantonese and can start on Monday. “I don’t have any friends like that,” admits the underling.

Well, if he was on LinkedIn, he might be able to impress his boss. The online business network earlier today quietly introduced a People Search beta. Once you opt in, a guided navigation panel appears on the right every time you search showing the breakdown of results across 11 different facets, including current company, relationship to you, location, industry, and whether or not they are looking for a job. By checking the appropriate boxes, you can narrow your search quickly and find who you are looking for.

They may be mysterious and perhaps even a bit shady, but secondary equity markets, which allow employees to sell off their shares to other buyers, are quickly heating up. Because of the rarity of IPOs and acquisitions in the startup world these days, early employees and founders are becoming increasingly anxious to convert some of their shares into cash (one need look no further than reports of employees selling Facebook stock at relatively low prices for proof).

Unfortunately, because these markets are trading shares of private companies, buyers and sellers are often left in the dark as to the worth of their stock. SharesPost, a private equity market that’s currently operating in public beta, is looking to help: the site has launched a publication platform for analyst reports meant to complement its equity market. And it’s offering a free two month membership to TechCrunch readers, which you can sign up for here.

As a teaser for what’s available on the platform, the site has shared two valuation reports on some of the world’s biggest social networks: Facebook and LinkedIn. You’ll want to check out the full reports here and here to read the full analysis and methodology (you may have to register).

LinkedIn has bolstered its position as America’s leading business social network by the month lately, with Germany-based Xing as the only company regarding itself a worthy competitor in the last few years. But now those days seem to be over – in the US and China, at least.

Today German newspaper Hamburger Abendblatt published an interview [GER] with Xing CEO Stefan Groß-Selbeck (who recently replaced founder Lars Hinrichs), and he revealed a couple of interesting tidbits of information about the future direction of his company (find a horrible, Google-translated version of the full interview in English here).

Talking in broad strokes, Groß-Selbeck said 3.5 million of the 7.5 million Xing members are based out of Germany, Austria and German-speaking Switzerland. This isn’t really that surprising, given the background of the company. But the interview also marks the first time a Xing representative publicly (albeit indirectly) admitted losing in the USA and China.

LinkedIn had a management shakeup last December – CEO Dan Nye stepped down. Founding CEO Reid Hoffman stepped in again and former Yahoo exec Jeff Weiner joined the company as President.

The hiring of Weiner as President was clearly an interim move, and we predicted he’d move into the CEO role sometime this year: “The addition of Weiner is also quirky, and may explain the changes. Weiner was likely expecting a CEO role as his next job. He’s now second to Hoffman. Perhaps the company is using the interim period to see how he can handle himself leading the company. I wouldn’t be surprised to see Weiner take the CEO job at LinkedIn sometime in 2009, or else leave the company.” It turns out that is exactly what happened.

LinkedIn continues to roll. They are the fifth most valuable social network according to our recent model. The site attracts over 15 million monthly unique visitors (Comscore worldwide, April 2009), up from less than 7 million a year ago, and has 42 million registered profiles. They’ve been ebitda profitable since last year and say they plan to be cash flow positive this year. In February, Hoffman told me “We can go public any time we want to.”

And Weiner agrees, telling me today that their current plan to to build an independent public company, with three key revenue sources: premium subscriptions, corporate solutions and advertising. To date the company has raised over $100 million. The last round, a year ago, valued the company at just over $1 billion.

It’s ‘official’; big shot CEOs are social media slackers. The hot news comes straight from ÜBERCEO, who says it conducted research on the topic for the past few weeks and has found that there’s little chance you’ll ever get to exchange pokes and tweets with Fortune 100 CEOs for the time being. Here’s the ‘miserable level of engagement’ ÜBERCEO has uncovered:

(after the jump)

Industry white papers, in general, are dull reading—unless you need a piece of information in one of them to do your job. Then you’ll pay almost anything (i.e. expense it) to get your hands on the white paper you need. Sometimes companies produce white papers and give them away for free, but they have a hard time finding the professionals who might be interested in whatever narrow topic the paper covers.

Enter LinkedIn. It knows what industry you work in and your job title, making it easy to guess what kinds of white papers you might actually be interested in. The business networking site is testing a new feature that turns white papers into ads and presents them to the narrow group of professionals most likely to want to read them. LinkedIn members can get white papers for free, and in return sponsors get qualified leads.

A year ago we modeled out the true value of various social networks based on the idea that users in high-value online advertising markets like Japan, the UK and the U.S. were worth more (financially speaking) than those in lower value online advertising markets. Facebook had recently become the largest worldwide social network in terms of users, but based on our model MySpace was still by far the most valuable social network.

We’ve now remodeled social network valuations based on current user numbers and Facebook’s most recent $10 billion valuation. The results are dramatically different.

Based on the original year-old model, if Facebook was worth $15 billion (their then-current valuation), MySpace, with far more U.S. users, was worth nearly $20 billion:

Our model takes Comscore data for available countries and regions. We’ve graphed each of 26 well known social networks with the data we have been able to collect. We’ve then calculated the average advertising spend (estimated by PriceWaterhouseCoopers in a recent report) for each person online in each of those countries. For example, in the U.S., the total 2008 estimated Internet advertising spend is $25.2 billion. We’ve divided that by the number of people online in the U.S. according to Comscore (191 million), to get an average Internet spend per person of $132. View the raw data and calculations here.

The U.S., by the way, is only the 4th most valuable market per Internet user, trailing The UK ($213), Australia ($148) and Denmark ($144).

How quickly they grow. Remember when Twitter was just a little pipsqueek, with less than 10 million monthly unique visitors to its site worldwide? That was back in February, 2009. Fast-forward to April, and Twitter’s U.S. visitors alone reached 17 million. Now comScore has released its worldwide numbers and it estimates Twitter’s global unique visitors in April, 2009 was a whopping 32 million, up from 19 million in March, 2009.

To put that in growth into perspective, Twitter has just passed Digg (23 million), LinkedIn (16 million), and the NYTimes.com (17.5 million) in monthly unique visitors, as counted by comScore. And comScore only measures the number of people who visit Twitter’s Website, not the millions more who send and read tweets via their phones, desktop apps, or other Websites. Twitter.com is also now bigger than Bebo and Freindster, for what it is worth. Who will it pass next?

Facebook, MySpace, LinkedIn, Yahoo and now Google. What do these have in common? If you’re reading this blog, you probably have a profile on all of them. And those are just the obvious ones, you probably have a bunch of other profiles on a series of other networks too. The situation has become untenable.

Imagine if you wanted to update one piece of information on all of them — like I recently had to do with a job change. That’s a lot of work for such a minor tweak. But if you don’t do it across the board, there will be incorrect information about you out there on the web. Information that is always just a search away.

The guest post below was written by Reid Hoffman, CEO and Founder of LinkedIn. Reid, who’s been a prolific writer lately, is a strong advocate of entrepreneurism and the startup mentality. See his recent Washington Post article Let Our Start-Ups Bail Us Out, and the guest post he wrote here on TechCrunch, Stimulus 2.0: It’s The Startups, Stupid. Reid has recently appeared on Charlie Rose, and we had a chance to sit down with him earlier this year for a video interview as well. Reid is an investor in over 60 web ventures including Digg, Facebook, Flickr, Friendster, FunnyOrDie, Ning, Last.fm, Six Apart and Technorati. He is also a member of the nominating committee of our upcoming TechFellow Awards with Founders Fund.

TechCrunch and Founders Fund announced the first annual TechFellow Awards last week. This is a great time to stimulate investment and recognize and encourage tech entrepreneurs –starting up is cheaper, talent is more fluid, and people are more inclined to take calculated risks. If we can find more ways to spur investment, it will be good for the entrepreneur now and good for society later.

As a serial investor, I’ve enjoyed backing some good Web 2.0 companies, and it’s helped me develop a shortlist of criteria to cut the wheat from the chaff. After five minutes of a pitch, I know if I’m not going to invest, and after 30 minutes to an hour, I generally know if I will. Many entrepreneurs are product-focused, which leads them to pitch the brilliance of the product. Others are money-minded, so they can over think the business plan. But neither of these approaches answer the first few questions I want to know as an investor:

Managing Groups in LinkedIn so far didn’t require a whole lot of management, nor was it very useful to those who created them. While other social networking services have long incorporated ways for group administrators to communicate more efficiently with their members, LinkedIn for whatever obscure reason never even bothered to create a feature that allowed admins to e-mail group members directly for the sake of sharing announcements.

I got an e-mail from LinkedIn just now letting me know that this feature is now finally being added, “in response to overwhelming demand from group managers” (no kidding) and that group managers can now blast out e-mails with announcements and create a discussion topic that members can comment on automatically in the process. As a privacy measure, LinkedIn is removing the ability to download or view member e-mail addresses.

uTest, a startup that allows companies to outsource their QA testing to ‘the cloud’ has just concluded its latest quarterly bug battle, during which it put some of the world’s largest social networks to the test. Hundreds of participants (many of which have been involved in product testing for over a year) did their best to uncover flaws across Facebook, MySpace, and LinkedIn, with $3,000 up for grabs for the testers who identified the most crucial bugs.

Below are the final results for the number of bugs found. It’s worth noting that this data is prone to bias and may well overstate the number of ’showstopping bugs’ (testers probably had a strong incentive to rate their bugs as ’showstopper’ so as to have a better chance at the prize). But it also meshes fairly well with anecdotal experience.

Angel and VC funding platform Angelsoft has launched an investor filtering tool, allowing entrepreneurs the ability to access detailed profiles on over 1,000 venture capital firms and angel investment groups in the U.S. Angelsoft allows startups to “push” their business ideas to over 400 angel investment groups and 15,949 investors across the world. The site formerly focused on connecting entrepreneurs to angel and early-stage investors only, but recently changed its model to include VC firms.

Angelsoft calls it an investor search engine, but it lacks a search box (a big flaw). Instead, entrepreneurs use Kayak-like filters to adjust their sorting results by how much an investment firm usually invests, what terms they typically offer, as well as by company-based criteria such as industry, location and stage. VC and angel firm profiles include a snapshot of the fund, industry expertise, prior investments, executive profiles and links to the LinkedIn profiles of investors. For the 450 investment groups that use Angelsoft’s VC and Angel dealflow management tools, the search engine results provide even more data, including a firm’s average response time to entrepreneurs applying for funding, number of applications a firm receives each month and additional past funding history.

Reid Hoffman is an entrepreneur’s entrepreneur. He worked at Paypal, founded LinkedIn, and invested in dozens more. Last night, he appeared on Charlie Rose, where he talks about the rise of social networking in general, and LinkedIn’s success in particular (it is adding one million professionals every 17 days and is emerging as a “low cost provider of really good hiring services”).

Yesterday, Hoffman wrote a post for us with some concrete suggestions for a Stimulus 2.0 plan led by startups. He hit some of the same themes on Charlie Rose. The best part of the hour-long interview, however is towards the end where Hoffman discusses the role that entrepreneurship can play in getting America out of its rut.

(Video, excerpts, and full transcript after the jump).