Information exposure in Google Buzz.
Regular users of Gmail have no doubt noticed the new entry just below their Inbox tag called Buzz - if you haven't yet, chances are you will soon. From what I can tell it seems to work a lot like Twitter and Facebook status updates do: there's just enough room to post two or three sentences, links to other pages, comments on Buzz posts, and other stuff like that. It also hooks links to other sides listed in your Google Profile (if you've set one up) so that if you update one of them, it automatically posts a link in your feed. Conversely, responses and comments to your Buzz postings get routed to your Gmail account so you don't have to keep clicking on one more tab in your browser. In other words, it's pretty nifty, albeit a little scary if you think about the privacy implications of this.
While we're on the subject of privacy, it seems that Google Buzz shows the names and/or e-mail addresses of the people you correspond with most often. When you enable Buzz (or just click 'cancel', like I did (that's right, it ignored my request to not set up Buzz)) it goes through your Gmail and Gchat contact lists, figures out whom you communicate with most often, and populates your list of followed accounts automatically. The downside of this is that someone can go to your profile page and click the 'Foo has x followers' and 'Foo is following x' links on the right-hand side and see everyone on those lists along with their e-mail addresses, thus revealing everyone you talk to with any regularity. In fact, if you read the Buzz announcement they tell you this up front. A little experimentation has shown that the person poking around also has to be logged into their Gmail account to see this, but that's hardly a hurdle. You can't make these lists private, so the only thing you can really do is unfollow them, which presents problems if you actually plan on using Buzz for anything.
obCommon Sense: If you don't want people to know about it, don't put it online.