I already quit it, but came back to it after a month. It was a planned return though, and I quit it cause I was spending way too much time (and energy and creation) on it. And I wanted to test my will.
Had to learn some self-control... I wonder if I'm better now, hehe. I sure click "Sign out" more often though.
ALSO, Facebook once suspended my profile for almost a month. I was nice, cooperated, and defended myself, so they apologized and restored my profile. Cool folks, those Facebook guys.
On accounts of privacy: I've set almost all the options to "Only friends" or even stricter now. Periodically, I relax privacy a bit if there are people who'd like to see a photo album of mine or etc., a note I've published.
I also quit played games on Facebook and have removed/blocked the vast majority of applications. There's only one I use, can't remember the name but I use it to keep track of my books, games, movies, etc.
Peace out.