Cory Doctorow has an article in Information Week which sums up a lot of Facebook and MySpace's shortcomings:
For every long-lost chum who reaches out to me on Facebook, there's a guy who beat me up on a weekly basis through the whole seventh grade but now wants to be my buddy; or the crazy person who was fun in college but is now kind of sad; or the creepy ex-co-worker who I'd cross the street to avoid but who now wants to know, "Am I your friend?" yes or no, this instant, please.The full article is here.
I think I'm going to delete my Facebook again. (And I'd delete my MySpace, except deleting it doesn't seem to work.)