I really like this post at:
My children are busy online at this moment. We have no parental controls on the web in our house. My older son IS the techdesk! I say that I am the parent and will intervene for them if they get stuck on any website with some wierdo. We have the medium settings at the moment on Google, I think...mainly to keep the results predictable in a good way.
All the books in our house are available to them. They may buy any paper freely should they wish to. I have the right to be shocked if I want to, but getting knowledge and questioning is their job.