Google turned its new "Buzz" social networking function on in my Gmail account today and I spent some time checking it out. Conclusion: it's got the privacy controls backwards.
While it's true you can decide whether to share your post only with a limited number of people, the default mode is to make it public for the entire Internet. If you are truly interested in protecting privacy, the default mode should be to share information only with the small group you have selected.
Deciding to go public should require an opt-in, affirmative decision from the user.