I know it seems weird to some people, but I'm friends with both of my kids on Facebook, and so is my wife. Our son is 20 now and is savvy enough to block certain posts from certain users and stuff like that. What he doesn't know is that he's in the same boat as his sister; he made the same mistake or simply doesn't think I'll bother checking. He has his laptop, but IE on the "kid's PC" goes into his Facebook account. Since he's an adult now, I feel kinda weird poking around in there, but mostly I'm just curious what he's bothered blocking from us. Typical stupid shit, of course. But he mentioned one time that he blocks us, which is practically an invitation to check it out, right? Plus, if he has a problem with it, I can always invoke the "my house, my rules" rule.
Our daughter's Facebook comes up on "the big PC" in IE, but I use Chrome to Facebook anyway. It's faster and renders things properly, and as an added bonus, her Facebook ID stays stored in IE.
As for it bringing us closer, there is that, but I try to keep it to a minimum. I don't comment on stuff that they post, because I'd just as soon let them forget that we're seeing it. I'd rather give them some rope and see what they do with it, plus I don't want their friends to get weirded out seeing their parents commenting on their stuff. We tag each other in pictures, and comment on them, and I'll Like things occassionally, but that's about it.