So, Buzz is finally out. We've been dogfooding it internally for a while and it's been great.
One of the best aspects of Buzz is the use of open standards. It's just feeds. And if you want to hook up a new data source to Buzz, it is just a matter of adding a link/@rel='me'. That two way connection between your profile page and the source is the proof that it is a source that you truly own. That's a pretty easy thing to do if you are a service provider, adding a little markup to allow integration with Buzz. And it's not like that information gets locked up; you can always pull the site connectivity information back out via the Social Graph API. Here is a demo site for querying the Social Graph API.
See DeWitt's post for where this is all headed and the other open protocols that are going to be integrated.