Facebook is a really good way to stalk people.
Knox College got facebook in the spring of 2005 and within days it seems everyone was on it. If you look at some people's user ID's in their profile URLs, you can tell how soon they joined facebook. For example, Graham Troyer-Joy's profile can be found at:
...indicating that he was the 106th person to join the site. 626 is the code for Knox; these three initial digits vary from school to school. More recently created profiles, or profiles that have hopped networks have a weird numbering system that I don't understand.
62600001 used to be a profile with a squid picture called "the creator". But now it's gone.