I think people get confused when we talk about putting the computer in a public area (not your child's bedroom) or reviewing the PC's history. We aren't talking about spying. What I'm advising parents to do is monitor their children's online activities but to do so OPENLY. Tell your kids what you are up to and ask about anything you see that you don't understand. I'm not a fan of covert efforts like keystroke loggers or hidden devices. If you are stooping to using technology to secretly discover what your child is doing online, I hope you know what you are doing. Should your child learn you've breached the trust bond between the two of you, it will be incredibly hard to repair that relationship.
I know there are people out there happy to sell you all kinds of spy devices for your teens. I just watched a Today show segment on secret keystroke loggers, GPS tracking systems and hidden cameras, not to mention drug test kits for your kids. Truly, I hope you and your children will always be able to stay very far away from ever considering needing any of those devices in order to feel safe.