So in effect, there are a ton of friends and acquaintances on there. A few months ago I was in NYC and wanted to hook up with an old friend of mine who moved out there, but I had lost her contact info. I logged onto Facebook, sent her a message, and lo and behold, 15 minutes later I get a phone call and we made plans to get together that night. Quite useful. For me, Facebook is pretty much just a social address book that populates itself instead of me having to track everybody down in real life, which I would never do. It's kind of a corner case, but that's what I use it for, and I won't delete it for that reason. Other than that though, it's pure hatred, and I'd love for everybody to be on a different service someday :)
I also didn't like how it really diluted the meaning of the word, 'friend'. People's friends lists would swell to huge numbers and some of them they would barely know at all ('we were at the same party this one time') or outright not like at all. I can see the benefits of having a service not unlike facebook, but for me at least the benefits seem to have become drawbacks.
It's kind of sad that when you are using a service just because you feel like you have to. I think that feeling creates a lot of resentment. I deleted my LinkedIn a few months ago, and it felt great.