Follow the link that facebook provides in its header: http://www.facebook.com/help/?page=219494461411349

It's very interesting. They straight out say P3P is a dead protocol. And from the explanation of how it works, it does seem to be a joke - trusting third party websites to honor user privacy ? seriously ? I think Microsoft is simply trying to raise a shit storm over nothing... at least Safari one is a real screw-up on Google's part...