Facebook is facing a backlash on their constant erosion of privacy. They have a privacy policy longer than US constitution, and a track record that has even sparked a federal complaint. While I'm a big believer in a transparent society I still believe users should be in control of who can see their information and how.

I think Qaiku, the conversational microblogging service, is doing this quite well. In your profile you have a simple setting:

Privacy of individual conversations comes from the settings of the person who initiated that thread. The setting is clearly shown in the sidebar. Some examples:

This way you can know who will be able to see your comments and make the decision before posting them.

The Terms of Service are not too tricky either, containing items like Be Nice and What is yours is yours.