Google Buzz posts a person's contact information on their public profile page.

For private investigator's looking for information, Google's Buzz could be a goldmine.
"Whether you call it a huge privacy flaw or just an annoyance, Google Buzz can put the contacts you automatically follow—a.k.a. those you most frequently email or chat—on a public profile page.
Google Blogoscoped's Philipp Lenssen felt he had to avoid following certain Buzz contacts, as he didn't want to expose his social circle to the wider net. He's right—by default, if you haven't touched your Google Profile, once you set up Buzz, those you're following, and those following you, are shown on your profile page in a right-hand link list.

Link: http://lifehacker.com/5469388/stop-google-buzz-from-showing-the-world-your-contacts