Feature Notes :
Note: Google Buzz had not yet been enabled for me through normal GMail Desktop access. These notes are based on my experience with the same by switching my Firefox user agent to iPhone and accessing the iPhone Google Buzz UI.
Has a very facebook / friendfeed like interface.
Comments : People can enter comments against a post which appear sequentially below the post.
Like : Has the Like feature also supported by facebook / friendfeed
Inline images and videos : Images and videos appear inline as a part of the stream.
No 140 character limitation : Or at least none that I observed
Each conversation becomes a web page. eg. the comment stream against my very first google buzz post.
The same conversation is also posted to your inbox. The conversation in the inbox gets dynamically updated as the conversation continues. A conversation that has been read earlier gets marked as unread when more comments are entered against it.
The conversation web page becomes an alternative location for participation. If say the conversation link is forwarded to others, they can immediately comment on (or choose to "Like") the conversation from the web page itself.
Private Channeled Messaging. You can mark posts as private but directed to a group of people. These groups are maintained and managed using Google Contacts. To the best of my understanding the future conversation is also constrained to the same group. Such messages are obviously not visible publicly. This is an excellent feature for closed group interactions.
Directed messaging is supported using the familiar twitter '@' style. However in this case you use '@' followed by the entire email address. Any posts made with '@' addressing also get delivered to the user's inbox.
Geolocation integration is supported. Thus you can view the public posts being made by people nearby you. Since I used firefox, it used firefox for geolocation support. I imagine and presume it would be using alternative superior mechanisms for mobile based conversations.
Comparison to Twitter :
One of the reasons I test drove Google Buzz was since I was wondering if it was a better Twitter. In many ways it is. But I don't think thats likely to be universally true. There is the 140 character simplicity to twitter which is its identifying feature. In many ways Google Buzz is a Friendfeed clone - not a twitter clone (with added inbox integration). I always found Friendfeed much superior to twitter for conversations and I suspect those who shared that perception will find Google Buzz far superior to twitter too. However it will run into the same difficulty that Friendfeed did. If the twitter user doesn't correlate his twitter account to the friendfeed account, it is very laborious in friendfeed to add a user you follow as an imaginary user in order to have his tweets appear in your friends stream.
I think where Buzz will take on Twitter .. and big time is the really large number of people who sign on to twitter, maybe make a few tweets and then say I don't get it and go away. I suspect most of them will "get it" on Google Buzz - especially if they have any Facebook experience (which is a large large set of people). In that sense while Twitter appealed to only a small set of people, Buzz at least has the potential to appeal to the mainstream .. and in that sense go for the jugular - Facebook's that is.
Comparison to Facebook :
Since facebook over a period of time has cloned its update stream to be like that of Friendfeed, it should come as no surprise that the Buzz stream is likely to look and feel quite similar. However two big differences stand out. The first is the way the social graph is managed. The social graph unlike facebook is asymmetric. ie. two persons don't have to agree to be friends to follow each other. In case of Buzz, the social graph is managed through google contacts. You can follow people who have public google profiles or follow anyone in your contacts. Thus if a person doesn't have a public google profile or his email address is not known to you, you may not be able to follow him/her. You don't need the other person's permission to follow. (At least thats the impression I formed, though I could stand corrected). The other big difference is the email integration. The entire stream and conversations are integrated into the gmail account. For most knowledge workers, I think these differences are likely to make for a more positive experience. In that sense - buzz is extremely well suited to be the Facebook of knowledge workers. Whether it can compete with the trivial, frivolous, chatty social networking capabilities of Twitter or Facebook is something I couldn't form a clear opinion on.
On carving a new market :
Based on my earlier statements, it should be obvious that I believe buzz will carve new markets which did not use Facebook / Twitter / Friendfeed earlier. These markets are :
People who tried twitter but didn't get it
People who primarily use email for communications instead of facebook / twitter (for both Personal and Business Networking)
People who would like to use Facebook / Twitter like capabilities from a knowledge working / business perspective.
People who are just too nervous to use anything new on the net may still find the email integration a continuum of their email exchange rather than a 'new web site'.
On Privacy :
I think Buzz definitely ranks superior on privacy, given its capability to conduct private directed closed group conversations. As an example, I can imagine many google apps installations which could use buzz for intra company conversations even as they clearly restrict even the public streams not to be visible outside the domain. While I haven't seen any comment from Google on whether buzz would be available for google apps, I imagine its only a matter of time since it is so particularly well suited for that environment.
On google wave :
Google wave in many ways was a damp squib. It imposed a new usability paradigm even as some of the capabilities such as near real time updates were clearly superb. Google buzz reverses the wave approach by offering a different conversation model which dovetails not only into similar usability expectations as defined by the competition but goes one step beyond by integrating into the killer web application - web mail. I wouldn't be surprised if it came to light later that Google buzz is a google wave backend with a completely new usability experience.
A note on integration :
While its only a statement of intent at this stage, google has setup a site for the Google Buzz API. However the promise is awesome in terms of multi standard support for variety of standards and protocols support including RSS, Atom, PubSubHubbub, Social Graph API, OAuth, WebFinger and Salmon. It does seem that google will want to support a variety of other alternative and mashup use cases around Google Buzz which might allow for more interesting uses to emerge (as it happened for Facebook and Twitter). Clearly a space to watch with some interest in months to come.
In summary :
Google buzz makes the strongest case for appealing to the power email users and those particularly focused on privacy (eg. knowledge working for businesses). Its strong differentiator is its mail integration. It does offer adequate features to compete with Facebook / Twitter for their existing markets as well. And joins the party with a large number of people - who already have a google account.