From PC Pro article:

"....
The Buzz app on the iPhone, for instance, uses the phone’s GPS radio to plot your every utterance onto Google Maps. Click the Nearby button in the Buzz iPhone app, and you’ll see lots of little speech bubbles appearing all over the map, pinpointing where people are issuing their updates from. And this isn’t only your friends or people you’re following, it’s anyone who’s using the service.
...."

http://www.pcpro.co.uk/blogs/2010/02/15/the-dangers-of-google-buzz-mobile/

The horrifying dangers of Twitter:

"...
Twitter let you publish messages that can be seen publicly on your profile if you explicitly set your profile public. And this isn’t only your friends who can read your tweets, it’s anyone who goes to your public profile.
...."

a-guy-who-writes-anything-to-get-some-ad-impressions.co.uk