BlogCatalog, one of the oldest operating blog directories is expanding with a with the beta launch of Social Search, a cross-network aggregation search engine that searches multiple social networks.

The Social Search feature is built on top on BlogCatalog’s Social Dashboard, which (like many services lately) aggregates member activity across other popular networks. The search feature allows users to search by single user, friends, or by anyone who has opted in to use the Social Dashboard feature.

I haven’t visited BlogCatalog in a long time, so I was surprised by some of the other features they are also offering. Personal news feed widget SocialStream allows members to broadcast their personal aggregated social network activity, wherever they place it, a similar function also available from Plaxo Pulse. This on top of a decent enough social networking platform that is built around a members blog listing and includes friends a topical group discussion.

Ultimately any site is only as good as the number of users it is attracting, and BlogCatalog is pumping through some great numbers, with comScore reporting just over 2 million unique visitors a month for the site on 6 million page views for both January and February. As the chart shows, this is significantly more than Plaxo, who offer some similar services. Newer aggregation services (including Friendfeed) were either not available or too small to be recorded by comScore so could not be directly compared. Alexa does provide some size and influence comparison here for those interested.

SezWho has teamed up with BlogCatalog, a social network of sorts for bloggers, to distribute its comment reputation system to BlogCatalog members.

BlogCatalog will provide a special version of the SezWho plugin that harnesses the data already stored in BlogCatalog user profiles to generate profiles for SezWho. While the plugin will be offered to all BlogCatalog users, SezWho participation will be necessarily opt-in (BlogCatalog does not host members’ blogs itself and therefore can’t impose SezWho on them).

The plugin will work with WordPress and MovableType 3 & 4, with support for hosted blogging solutions coming later in the form of a JavaScript and OpenID-based solution.

It’s important for reputation services like SezWho to establish these partnerships, and to support the widest range of platforms, because reputations are not terribly useful if they are restricted to a small segment of the web.

We currently use SezWho on CrunchGear to track reputations there. You can see our previous coverage of SezWho here.