We had a lengthy correspondence last year with a company called Streakr, which aimed to provide search across social networks. The August 2006 launch didn't seem to go ahead, and the holding page remained.
However, it seems that Streakr has now quietly debuted, offering a slick-looking way to browse social networking pages using an iFrame. You can browse Bebo, MySpace, hi5 and Facebook in a StumbleUpon-like setup, plus lots of other site genres.
There's also a toolbar for searching from within your browser, and the search feature is very similar to the one on Wink, enabling cross-network search for certain users. User ratings are also included, and you can create a profile page on Streakr itself, similar to SocialURL.
It's a nice attempt, but it's hard to see how they'll get traction without referring masses of traffic over from the other networks: perhaps widgets (like the Wink Widget or ShowYourself) would help there.