No, and I never ever ever intend to. For one, I find the appeal of social networking to be bizarre and inexplicable, and quite frankly narcissistic. But even supposing I wasn't convinced the entire concept is a useless fad I'm better off avoiding, I would never contemplate using the Facebook.
Why? Well let's just say their founder and I have fundamentally incompatible views on the nature of privacy - I would go into more details, but that would require communicating almost entirely in expletives and I like to think I have some measure of class.
So yeah, Facebook is right out.