I don't believe in it either.
I think people should learn from them. Hell, I know I have . . . er...most of the time.
I think, if my parents grounded me, I would probably react the same way I get when teachers tell me to stop doing something. I would go out of my way to piss them off completely! Haha, no logic in it, I know. But I just hate it when people get mad at me for the little things that I do.