I found a very interesting social networking site, SciLink.com. The idea was simple enough, they mine scientific publications to find links between co-authors. All you have to do is to sign up on their website, claim the papers that you have published, and you can see a collaboration network with you at the center.
They have some nice visualization tools on the site. But with my limited experience I have to say that this is not ready for prime time yet. The publication records in their data base are limited (mostly based on my searches of some big names in my fields). It's hard to imagine that people will go through the trouble of entering all publications by themselves. Also this probably won't work well before there is a critical mass. I will check back on this site sometimes later and hope that they are on their way to a healthy growth.