I only add people that i really know, or have known a long time ago, and know that it WILL be good be in contact again. Otherwise I just ignore the requests.
FB can be used well and sensibly. The user really determines if it gets silly/obnoxious etc...
If i do add someone who turns out to be annoying/obnoxious, the "hide' feature works great - one click and i never see that person or his/her posts again - i have done that perhaps twice so far since i started FB.
I am very glad to keep in contact and share photos and news with a lot of relatives/friends that live in other countries and also some school friends that i am in contact with again. FB really is good for things like that, and the chat feature is really nice when you can do it with people that live far away/overseas.
bottom line: user determines how well/bad FB experience is. It's very customizable, so there's really no excuse to not to make it work just the way you like it.
Some people just say 'I hate FB' as if it was a fashion - it's possible that they have no use (like i described above) - but that's not FB's fault, nor does it mean that people cannot use it in a serious/sensible manner. And one can do it without being on it ALL the time, for sure.