I'm right in the demographic "sweet spot" for FB, but it still took me a while to get into it. Actually, it wasn't until my in-laws of the older generation really got into that i was able to adopt the whole thing. It's a great way to keep family posted on stuff (will hopefully replace the Christmas-update letter...), she pictures, etc.
It's also nice when old friends you've lost touch with for years find you and you can catch up a bit. If you don't want to talk to them, just ignore them.
Really, when it comes right down to it, it's like any other message board we use, but with fancy features and the ability to see posts from only the people you know.
That all said, it's really not for everybody.