I use it but there are a lot of things about it which I really dislike*.
I would quit it, but the problem is, so many things get organised through Facebook, I think I would miss out on a lot of social events without it.
It would be ok if noone used Facebook, because people managed for an awful long time without it. However, now that Facebook has replaced certain functions (eg. mailing invites, keeping an address book, writing to/calling people you don't see that often), I think I would lose out if I quit.
*the stupid groups and fanpages and the people that like them, how easy it is to stalk people, increased difficulty of keeping secrets or even privacy, the cheap version of friendship/social interaction it offers, how the relationship status has importance, how some people don't quite realise the impression that they give off online (guys with shirtless profile pictures, girls with 3000 pictures of themselves, people's descriptions of themselves which sound like CVs) etc.