Here are a couple of links on the statistics about Social Networking Sites (SNSes)
Facebook user statistics:
-http://www.facebook.com/press/info.php?statistics
-http://www.checkfacebook.com/
A list of the most popular Twitter users
And the latest SNS (or something equivalent to it) to hit the streets: Google Buzz! For those who have yet to try it, it's in your GMail account. Here are a couple of sites that talk about Google's attempt to rival Facebook:
- http://mashable.com/2010/02/09/google-buzz/
- http://gizmodo.com/5469056/google-buzz-ad-parodythis-is-a-parody-right