I strictly control the amount of time my children spend on the Internet, and I also strictly control what sites they can access and from whom my oldest daughter (the only one with email) can receive email (three cheers for Mac’s great parental control features!). I think this is just part of being a good parent. There is no question in my mind that, along with so much of the garbage to be found on the Internet, just using it can easily become addictive, especially for someone who is not yet mature enough to handle it.
However, in China, they seem to have taken things too far: they have “Internet boot camps” in which physical means such as beatings and electro-shock therapy are used to cure teenagers of Internet addiction. Fortunately, the government there has stepped in to ban these practices after a teenage died at such a bootcamp.