Yahoo Buzz allows you to let people know what stories you think are important and therefore worth sharing. So whatever you do in Buzz (buzz a story up or down, post comments about a buzzed story, etc.) is public, unless you change your Buzz Activity setting to private.
When you’re the first person to “buzz up” a story, within Buzz, your name and avatar display next to that story, along with a link to your Buzz Activity Page. On the My Buzz Activities page, you’ll see numbers next to First Buzzer, Buzzed Up, Buzzed Down, and Comments, which indicate how many times you’ve been the first one to buzz up a story, and how many stories you’ve voted to buzz up and buzz down.
To keep your Buzz activity private, simply uncheck the My Buzz activity is public on Buzz checkbox. As long as you’re signed in to your Yahoo! account, you can see this box from any Buzz page.