Today at the Web 2.0 Summit in San Francisco, Twitter co-founder and CEO Evan Williams took the stage for a discussion with Federated Media’s John Battelle.

It was a lengthy discussion covering a lot of interesting topics. If you’re interested in Twitter, you’ll probably want to read the full Q&A below (and we’ll post a video if we get it).

For an overview, Battelle at first focused on revenue. Williams notes that while Twitter is definitely thinking seriously about revenue, 97% of its efforts are still on the product and technology (which he thinks will be key for revenue eventually). That said, they are thinking about ways to charge brands that use Twitter (which everyone has known for a long time), but that they’re also still open to some advertising ideas too.

In terms of Twitter’s recent growth slowing down, Williams acknowledged that traffic to twitter.com in the U.S. is slowing down for now, but said that they think they have new features coming out that will change that. He also noted that while that growth may be slowing, they are still seeing big growth in both mobile and abroad.

Williams said that he doesn’t regret the decision not the sell Twitter at all. He acknowledged that they’d been meeting with Facebook since he took over as CEO almost exactly a year ago. But ultimately, he believes they can do great things with Twitter, and he doesn’t think being a part of a bigger company will help that (this drew applause from the audience).

Williams also doesn’t think that Facebook has to die for Twitter to survive, and vice versa. He sees the two as doing different things, even though there are some similarities. Interestingly, Williams also wasn’t sure that Twitter and Facebook weren’t talking about a way to link up their data. He said he’s not involved in those dicussions, but seemed to indicate that they may be taking place.

When Battelle asked about Google Wave, Williams said he thought Wave was “awesome.” He also noted that if he weren’t doing Twitter, he thinks he would be doing something similar — working on the problem that is email.

The most interesting bit came at the end when conference founder Tim O’Reilly asked a question from the audience. O’Reilly asked if it was time to retire the Suggested User List (SUL) with the new Lists feature coming? Williams made it very clear that he absolutely agrees that it’s time. When Lists comes out and are working properly, they plan to kill the SUL, Williams says.

Below find the full Q&A (paraphrased):

JB: What’s your revenue model going to be?

EW: We’re thinking about it, you can’t raise as much money as we have without thinking about it. We’re spending 97% of our efforts still in improving the product and technology. It would be a mistake to take our eye of the product and focus on the revenue right now. That answer it?

JB: No. (Laughs). So what’s the revenue model.

JB: With search, what if your revenue model was little links all over the site and to the third party guys?

EW: I like where you’re going, we’ve never thought of that. Hasn’t worked for anyone else (laughs).

JB: Mobile (SMS) is a revenue source, and there are a lot of brands that want to work with you. Brand marketers? Is that something to consider?

EW: Yes. Not first though. I can tell you that we’re optimistic about revenue. There is some advertising that makes sense for Twitter. Twitter isn’t a social network, it’s an information network. It tells the world what you care about. Brands use it to drive sales, driving foot traffic, or move old inventory. Eventually we’ll be able to extract value for ourselves.

JB: What about some business services? Share the data you have about users?

EW: Yeah, I find that interesting. There are some users trying to do different things. In broad strokes, there are business and personal users. Business users may want those things. We can charge money for that, and it will get them using Twitter more. Data will be a big part, but not the only part. And that will be a platform too. Comcast doesn’t use Twitter.com, they use a third party app, so we have to work with them with this too.

JB: Twitter’s growth has been extraordinary, but the past few months it has trailed off. I know it’s only a slice of the data we can see, but comment on that? Is Twitter dead?

EW: We are seeing slowing growth in some areas, and accelerating growth in others. The big two areas for growth are mobile and internationally. Through our API and third party clients is a very high percentage of the traffic. But U.S. Twitter.com traffic has slowed for now. But we’re launching stuff that we think will pick that back up.

JB: People are confused when they come to the site right? The suggested users aren’t always the best. How do you address the ‘what do you do question?”

EW: It is a problem, but it’s an upfront problem. We haven’t spent much time on helping people find the killer app of Twitter for them – we’re focusing on that now. I’m very excited for the Lists feature for that reason. It drives discovery for both new and old users. Lists also filters for people following too many people.

JB: Let’s move on to Facebook. Why’d you turn them down? And maybe Google too? Have you ever woken in the middle of the night saying ‘I should have taken the check from Facebook?’

EW: No.

JB: What made you think with this one is the one you’re going all the way with (having already sold other companies).

EW: It’s both Twitter and where I am as an entrepreneur. I took the CEO job almost a year ago, that’s about when I realized it was getting really big. That’s also when I first talked to our friends in Palo Alto (Facebook). I didn’t see a reason to sell. “Business is a context for doing interesting things.” The number of cool things we can do with Twitter blows my mind. Going to a bigger company doesn’t make that better. (Applause)

JB: But now Facebook is becoming more like Twitter. What do you think of that?

EW: I don’t know how Facebook’s feature prioritization works. I think they probably came about it the same way as us. They came up with the News Feed, we did something similar, then they changed again. For their size, it’s impressive how they can change. “I’m pretty sure the world is big enough for Facebook and Twitter.” Facebook is for something different, it’s about your close friends.

JB: What do you think about Google Wave?

EW: I think Google Wave is awesome. I think what they’re trying to accomplish is awesome. I might be working on something like that (reinventing email) if I wasn’t working on Twitter. I don’t know what it will be – that’s similar to how Twitter started. I like that there is a way to tweet from Wave.

JB: MySpace and AOL sync with Twitter, why not Facebook?

EW: I don’t know, that’s on their side. It’s possible that we’ve been talking about that, but not me personally. Syncing isn’t always the best user experience though. It’s different uses, that’s why all these services will survive in most cases.

JB: Is there a business model for the third parties? Can that ecosystem support them long term?

EW: We need to get better about that with our third party developers. We can do better, we do it a bit. We are working on terms of service for the API for this. They need more than ‘don’t worry, you can invest in us.’ Developers are crutial to where we’re going.

JB: I haven’t seen the Fail Whale often lately, but there is still grumbling about stability. Twitter is large now, but not huge. Are you concerned about scaling.

EW: I’m not as concerned as I used to be, but I’m not satisfied with where we are. In the last year, a lot of the core problems got fixed. There are a few pieces that we still have to fix. Reliability is something we’re still working on after scaling – we’ll be working on that for a while.

Question From Audience: What about users who get suspended for no good reason?

EW: That’s unfortunate. We’ve had overactive spam killing scripts in the past that have accidentally removed people, which we’ve apologized for. There’s a lack of information still though, we need to be better about that.

Q: What countries or regions are really popping right?

EW: Top 5 active users are U.S., UK, Brazil, Japan, and Indonesia. Not sure which is the fastest. Brazil is moving fast. New launches in India and Japan in mobile should help growth too.

JB: What about the celebrities? What about Hollywood no-Twitter clauses?

EW: I’m not too worried about it. I was talking to the guy who owns the Patriots – he loves it and the fans love it, but he doesn’t want his players giving info to other teams. Same thing with celebrities, they don’t want deals to be killed.

Q: Why have a DM daily limit?

EW: I didn’t know that is a problem people are having. I can look into it.

Q: As a journalist, it blows me away how Twitter is changing the way we get information. Are there any tools you think you could give us?

EW: I’m glad for that usage. We’re putting a ton of effort into search and discovery. We’ve just scratched the surface on it. We need to be more intelligent about mining this data.

JB: Search deals with Google and Microsoft?

EW: What deals? (awkward) Seriously though, we think third-parties can come up with great tools for people in the media.

Q (from Tim O’Reilly): For a long time there was only one list, the SUL. Is it time to retire it?

EW: Yes, it’s time to retire the SUL. It was a quick fix to a problem. We want to kill it when lists come out.

Q: Will these features kill third-parties?

EW: We don’t think so, we think this will help them.