We (community) should keep an open source database of what is banned. It would be insightful. For example any youtube comments mentioning "Open Street Maps" are automatically deleted ~30 seconds after commenting (very sneaky, the commenter might not even notice..).

Imagine what you could tell about a company by knowing what they don't allow their employees/users to talk about.

EDIT: also relevant, Paul Graham's essay What You Can't Say

http://www.paulgraham.com/say.html