This came after I learned that it made no attempt whatsoever to be Twitter API-compatible.
It violates the prime directive of new software. It starts turned on, and the way to turn it off is all-but invisible. And it invades a space that heretofore Google helped to protect. One of the big values of Gmail is its spam filter. Now all of a sudden it's as if the exhaust was reversed, and it was spraying dirt into my message stream, instead of filtering it out.
New software should be easy to try out, and there should be no penalty for doing so. Here, they didn't even give us an option, I was automatically signed up, and the way out was hidden. The first bit, which is fun -- create a new post -- is followed by a flood of new messages in a semi-sacred private place, my email inbox.
Bottom-line: There's no good reason why Buzz (terrible name, btw) should be integrated with Gmail. The company showed the worst judgment. It took what was the industry leading web mail product and turned it into a lab experiment. Once I turned it off (it's not hard, there's a switch at the bottom of the Gmail home page), Gmail went back to being Gmail, and not a nightmarish ad for Google's software design ineptness.
After all that, Kevin Rose's analysis is right on. He calls them feature requests -- clever -- but his concerns are so basic, it's another way of saying this should have been labeled pre-pre-beta and should have been opt-opt-opt-in with disclaimers and confirmation on confirmantion, instead of turned on by default for all Gmail users.