At one time I had facebook, but I decided to get rid of it. I think it was a great way to communicate with a group of people, especially while I was in school. I also think it can be a good too to use in helping some people, but for me those weren't good enough reasons to keep it.
I didn't like and I found that....
1. I would get friend requests from people that I may know of (went to school with), but don't even talk to when in a large gathering. What's the point of befriending someone if you don't talk with them outside of facebook?
2. The game notices and constant news feed of people got annoying. (Especially from those that use it to announce every event of their day as it's happening or to let us know how they are feeling every half hour.)
3. I don't really want to know about others lives, UNLESS they themselves tell me.
4. I'm a private person, I don't feel the need to share a bunch of stuff with a group of people, even those that are friends and family. I prefer to share that on a more personal level.
And finally, it seems as though a second or new side of people come out online and I don't care for that.
As far as teenagers using it, I think as young teens internet time should be monitored and watched by an adult. I have 10 year old students that have facebook and I don't think it's wise to allow that young of children to have an account. I think that if married couples want facebook, it's best that they share an account. It's the easiest way to avoid any curiosity, hurt, anger, jealousy and lots of other things that facebook could cause.