I must confess. I am on facebook. I used to be on myspace, but that was initially for a good reason. See I had to hack into a young lady's myspace account on behalf of her mom because that foolish young lady (all 12 years of wisdom) had taken some unsavory pictures of herself for her friend preceded by boy. So this distraught mom wanted to find out what her daughter had been doing and prevent any future permanent ramnifications for her.
People just don't seem to get it, and of course you can't expect kids to get it. The internet, once you post something to it, is a permanent record. And it will be your legacy. And it very well maybe used against you one day, by a potential employer, by a prospective love interest, or by law enforcement. Kids post the darndest things. They think they are having a regular conversation and say whatever comes to their minds. the good thing about verbal conversations, especially those really pointless ones where we may say the stupidest things, is those tend to get forgotten, and there is no permanent record of them. But the internet has its own memory, one which won't go away any time soon.
Here's a great example, Mr fabulous drives drunk and hits and almost kills someone. A few days later he goes to a party dressed as a jailbird. Mr prosecutor gets his hands on the pictures courtesy of none other than facebook on the internet, and the rest is history.
http://www.cnn.com/2008/CRIME/07/18/facebook.evidence.ap/index.html