It comes with the announcement banner "Go beyond status messages!!!". I would rather put it as "Go towards Facebook!!!". And as soon as i saw this banner when i launched Gmail, it just reminded me of something called "Google Wave", something which has become the past now (atleast for me). Seriously, it took lot of requests for me, sending to lot many ppl, to get into Google Wave community. But now, i hardly (almost not at all) type "wave.google.com" in the address bar. A separate url, just for some 'broadcasting' yourself stuffs, was the main reason, for me not to visit there often.
Google Buzz, exactly solves that problem first, by direct integration into GMail. I don't have to go anywhere else, to Buzz, which gives me total relief. They say Its "a new way to start conversations about the things you find interesting and share updates, photos, videos and more.". I agree with all those words in that sentence, except "new" , just because these features that Google Buzz offers are already tried, tested and a big hit in one of the most popular Social Networking Site, Facebook.
Still, one big feature, which differentiates this with its competitions is, "Built Into GMail" thing. GMail has transformed communication in www, by evolving from just another email site, adding chat (i still 'Unlike' the Invisible mode feature in that :( ), video chat, and lot other stuffs, now this Buzz. I really like this Buzz, just for this feature. But there are really lot more features coming with this Buzz. You can check it here.