I have an account on LinkedIN.
I have an account on Orkut.
I have an account on [name the social network site du jour here].
I think you get the point, right? This is getting really old. Social networking has moved beyond its initial phenomenon stage and is now a genuinely useful tool. As with many things today, the data aggregator is the winner and NOT the owner of said data (see this interview for an excellent reference point on that last statement). So, who will aggregate all of these social networks? Google is trying.
While not live quite yet, Google Operating System has an excellent summary (with a link to an unofficial press release) on OpenSocial....Google's name for their plan to aggregate social networking data using a series of API's.