I spent my first forum experience holding people up to the standards of real life.
I learned my lesson and spent almost two years staying away from the internet as a result of the evil that can spew out of people when given a notion of anonymity.
Now I maintain a certain amount of privacy. Talk little of my real life except in abstractions that can't really lead to me, and most importantly, that can't be used as barbs to tear at me with.
The internet can lead us to some wonderful people. But we have to show such extreme caution in taking them at face value until their true nature is proven. It's unfortunate, but it's the truth. And frankly, if a kid can't understand that (and few can IMO), they probably shouldn't be on social networking sites unless it's with people they know personally (like grandma, aunty, and REAL friends).