Bruce Schneier has made a fuss by writing about how he leaves his wireless internet open. As a well regarded security expect, how can he do this. You'll see many arguments for and against in his posting. I'll expand on one of mine.
Part of Bruce's argument is one I express different. I sometimes say "Firewalls are a hoax." They are the wrong choice for security, but we sell them as a good choice. Oddly, however, this very fact does make them a valid choice. I will explain the contradiction.