I have used Buzz for a month now and I'm quite satisfied with its functionality. IMHO Google Buzz is way different from what we all thought and is much more sophisticated. Buzz is some sort like Facebook operates in Twitter mode, that is, conversations and social interactions are made in Facebook style, but the social connection model is Twitter's public follower/followee style.
I feel that Google Buzz was already designed for public communication since it is launched. Currently I'm following 90 people with professional Google Profile who I think have use Buzz in the correct way. By professional I mean, these people write meaningful microblog posts that span few paragraph, share interesting links that talk about technology, and have meaningful discussion with their followers. I think the private features are just minor side features that allow some private communication, but Google is not really interested in that and the private features have proved to be more troublesome than is useful.
Google Buzz is just so much cooler than Twitter when you use it in a public way. You can post messages as long as you want, no 140 characters limit on Twitter and 420 characters limit on Facebook; You can write comment directly on someone's Buzz post and seen by everyone directly; You can embed links, photos, and videos directly in your Buzz post - no more short URL; You can "retweet" someone's Buzz post easily by clicking the reshare button. When Buzz is so powerful, I just don't see the point of using Twitter anymore.
Behind the scene, Google Buzz is also significantly different than other social networks. The protocol behind Buzz is really just the core product Google is creating, and Google Buzz is expected to be one of the providers within the decentralized Buzz social network. Google has developed various technologies such as PubSubHubbub and Salmon protocol in hope to create a public, open, and decentralized social network, but we all fail to see the true value behind Buzz. Still though, I don't really like the current Buzz protocols, and I think there are better ways to build such protocols.
Google Buzz also has significantly improve its privacy settings since its troublesome debut. When I first used Google Buzz, Buzz will notify me that the stuff that I'm doing is public whenever I first time made public actions such as posting public message, comment in public posts, follow other public profiles, like or reshare a post. And to avoid people confused on the publicy of their actions, the privacy scope is shown clearly in each and every post. It even states clearly on resharing that "X people publicly reshared this". Sometimes I even found it too annoying and thought, why don't Buzz says "X people publicly liked this" as well.
I think the biggest mistake Google Buzz has is its integration with Gmail. Google first introduced Buzz through Gmail in the hope of gaining market share through Gmail - HUGE mistake. There is a fundamental mismatch between Buzz and Gmail - Buzz is public oriented but Gmail is private oriented, and when public features are mixed into private account, disaster happens. While I am happy to have a public Buzz profile, I don't necessary want to correlate it with my private Gmail profile. That's why I created a separate Google account just for the use of Google Buzz. Now it's not that I have embarrassing stuff associated in my email account, but I want a way to clearly separate my public and private identities - albeit a weak separation that people can still find out the link if they want it bad enough because I made no effort to hide the link. We just need a way to separate identity from account - so that we can create multiple identities (persona) in one account and associate the identities with different purposes and privacy scope.
The other problem of Buzz integrated with Gmail is that the UI sux. Google Buzz is no way similar to Gmail, and forcefully cram the Buzz interface into existing Gmail interface is stupid. It would be much better to move Buzz into a separate page, to make both products less bloated.