I was on Facebook until recently, when I decided I was fed up with the inane trivia that constantly dribbled down my timeline thingy, so I terminated it. I have Twitter, but don't use it much, and I recently also killed Linkedin, as I didn't like how it seemed to contact all my 'friends' by itself.
The one other, which I (currently) rather like is Google+. It seems to be much more controllable in what you see/don't see, and I can log on and see topics of interest to me, rather than reading about how someone has just taken a dump in their new toilet. :uncomfortableness: