Just as a nitpick: "the messages can be larger" is an anti-feature for me, and for many others that use Twitter. Inline images and videos is one thing, of course, but if longer messages was a feature then blogging would have defeated Twitter before it launched.
Most people can't figure out RSS readers, and twitter lets you read and write in the same interface. Everything else about twitter is an anti-feature, including the post length limit.
The main reason for the 140 char limit is SMS. When it launched, Twitter was mostly a way to do a sort of SMS listserv.
I wouldn't call the 140 char limit an anti-feature either. Its become a key differentiation point, and is in many ways what makes Twitter Twitter.
You can say a lot on 140 chars, also if something's junk you know quickly to not read it. It also doesn't take a lot of screen room, thus there's a lot of data available without a scroll down.
It would be interesting to have a 140, 700, 5000, unlimited character filters in Buzz. If its display algorithm was used well, it could work out if long posts from a particular person were usually not worth reading to most people.
It's taking the best of the Twitter ecosystem, Twitter, Friendfeed and putting it into Google's social graph. It's innovative with the combination of features they've chosen to employ, but it's not original, though. Search was never new when Google started either, remember.
-- edit: I am going to use Buzz to start blogging again. Instant viewer base, who I can identify.