One word: LinkedIn.
Pretty addictive professional networking site, kind of like friendster and Orkut, but definitely geared more towards professional networking. Concept is like a Kevin Bacon six-degrees-of-separation thing, and you can only see people up to four degrees away from you (I think). Oddly enough, by the time I added my second connection, I found people that worked at a company I did back in 1997-1998. Talk about a blast from the past.