Cory Doctorow has been writing about Net filters for the Guardian
See no evil?
"every filtering enterprise to date is a failure and a disaster, and it's my belief that every filtering effort we will ever field will be no less a failure and a disaster. These systems are failures because they continue to allow the bad stuff through. They're disasters because they block mountains of good stuff. Their proponents acknowledge both these facts, but treat them as secondary to the importance of trying to do something, or being seen to be trying to do something. Secondary to the theatrical and PR value of pretending to be solving the problem."