I had a FaceBook account, but started seeing the writing on the wall - the stalking that you see, the targeted ads, the government getting involved, etc - bailed out with 5 minutes notice to my friends. Pretty much said, if you have my email address, you're important, if not, you've got 5 minutes for me to think about giving it to you. *poof* - done.
That was 2 years ago and I haven't looked back. I don't belong to any of those sites now and I won't do so later either. I actually go so far as to block FaceBook's URL on my local firewall so I don't even have to see that crap. I would block it from the entire house, but my wife does log in about once every 4 months to check up on old friends.