I used facebook when it was closed, and used by college students. It was a great way to find people in your class to ask a quick question about an assignment, schedule, etc.
I closed my account when they opened it to everyone.
Even when I had it, though, I never went on. A major pain in the ass, and a time waster.
I should also add that I am a selfish asshole, and prefer to not have contact with random people from my past who don't care enough to keep up with me the old fashioned way. The friends I still maintain contact with are people I truly consider friends.