I wonder that too.
My kids are allowed on the internet, with my supervision. I have access to everything they view or join. They have to ask me before they can sign up for anything, and even my son, who is almost 14, asks every single time.
Between the two of them they spend less than 1 hour a week on the computer (for fun, not homework). But to be fair, that's probably because I'm on the computer talking to all of you. ;)