Although it is easy to blame MySpace, etc., the Web per se is not the problem. Unfortunately, the Internet has made it a lot easier, not just to conduct legitimate business (correspondence, shopping, research of all kinds), but also to do nasty stuff to innocent kids.
First, these sickos can connect with like-minded types & reinforce that what they're doing is OK, normal stuff. Second, finding potential vicitms in chat rooms, MySpace, is made much more simple.
However, as several earlier posters have related through their stories, it is not just something that cropped up with the advent of the Web a few years ago, but these pervs have been plying their trade probably throughout human history. Let me share 2 stories, both from about 1978.
First, the two 4th grade classmates went to visit a local barbershop on the way home from school (the proprietor was a prominent church member). The first couple of times, the "kind" barber gave them candy, but it didn't take long for the porn to come out. The minute one of the girls told her mother about it (thank goodness for that child's sense of "something isn't right" and the open communication lines!), that was the end of the trips to the barbershop and, soon after, the friendship.
Second, the almost-eighth-grade graduate picked up the telephone one day. The male voice on the other end asked, "Is this [Jennifer Jones]?" "Yes". "I'm [Salvatore Vinnelli] from the Barbizon Modeling Studio, and we are interested in doing a photo shoot." (pause) "I need to ask you a few questions first." "OK" "Do you have any hair under your arms or 'down there'? "Uh, I don't think I need to answer that." SLAM.
I guess my "take-home" thought for the day is that although vigilance is important, we parents also need to give our kids the (age-appropriate) tools to realize when something isn't right, and that they can come to us and we'll help them through.