Stop Google Buzz From Showing the World Your Contacts - google buzz - Lifehacker.
If you are a person who values their privacy and want to secure you Google Buzz contacts, I.E. Not show everyone in the world who is in your contact book, follow the directions above.
I've done this, just for good citizen's sake, as well as manually blocked some people that I don't trust. Keep on top of this stuff people! As an online community becomes more ubiquitous, the more risk you present in revealing too much.