A lot of people compare Google Buzz to Twitter. On the surface, it looks more or less the same, where you multicast some sort of status. But I think there's some fundamental differences that make the usage a little different.
Buzz enables public conversations that you can see all in one place. In twitter, everyone can be talking about something, but most clients don't show this view unless you explicitly search for a particular hashtag. And peoples' replies to a status is fragmented across the board--if you don't subscribe to someone, you can't hear what they're saying. So conversations are regulated to people that know each other directly. Buzz and Friendfeed takes it one step further and make a semi-public conversation between friends and friends of friends possible.
Friendfeed's insight is that people like to converse around something and making it easy to come up with topics. In fact, Friendfeed--and subsequently Google Buzz--are basically forums and bulletin boards that have really lightweight thread creation. So lightweight, in fact, instead of having to come up with a topic, you have topics implicit in the activities that you do online. Posted pictures on Flickr? Your friends can talk about it, even if they don't know each other. Listening to music posted on your gchat status? Your friends can make other suggestions or berate your bad taste.
What Google was able to do that Friendfeed needed a couple years' of traction to do was to tie it to already existing google services without asking. That provides a lot of topics of conversations without setting anything up and people can get started right away.
Facebook has all the mechanisms I've described above, with the exception that culturally, it's private. I've rarely seen friends of mine talk to each other through the commments unless they know each other already. Google starts semi-public, and it gives people permission to talk to each other, even if they don't know each other. That, I think is a plus.