I have one. Started an account initially so I could get an idea of who my roommates were and contact them. Over the years I've gone back to just using e-mails, and I suspect that after I graduate, I'll delete the account as I have little use for it.
I'm not too keen on the whole thing. Mostly because within a week of making an account, every freaking person I ever said "Hi" to in highschool started trying to add me as a friend. A lot of them I just forgot about and still have no emotional connection with them. I even think I should go back and delete half the people I did decide to accept on a whim because I never contact them and they never contact me.