An excellent article, and a most important one. It is a crucially important subject for parents and teens alike. I am glad you didn't stress the need for filtering software as the end-all answer to this problem. Filtering software is something like an arms race. Every time the filter makers come up with something new, the porn sites find a way around it.
Filters give parents a false sense of security.
You make an extremely important point about casual chatting being potentially dangerous. I read an article about a man who spent his free time surfing and talking to teens. It gave the example of a 14 year old girl in a somewhat distant town. He made her very nervous, to say the least. The man then called her parents, and arranged a visit.