Earlier this week Google launched Buzz, an extension to Gmail.  Google launches lots of things – some work – Maps, News, Gmail, some don’t, or haven’t yet, like Base and Wave.
Buzz works as a status stream, like twitter or Facebook.  You write a short message, spreading news of even just saying what you’re doing, and this can be seen by your ‘followers’.  You can also link your other sites to it, for example a blog, and also get it to automatically update from your twitter stream or Flickr account.
See a video of Buzz in action here:
It’s easy to see why they they’ve done it.  Social is perceived to be the big thing at the moment, and Google don’t currently have a world-beating social service.  Their won network Orkut is popular in Brazil and India but not really elsewhere.  However Gmail has 176m globally (according to comScore), and is designed to allow people to both share and also manage social relationships.  
By adding Buzz they are moving these people into the territory occupied by Facebook and twitter, but also local and location-based services like Yelp and Foursquare – apparently Buzz works very well on the mobile too.
Having tried it I’m not sold on it yet.  I rely very heavily on my Gmail – I must visit several times a day, and sometimes it’s hard to keep the unread emails to a manageable amount.  Buzz gives me something new to check and keep a handle on.  It doesn’t look as nice as twitter, even though you can add pictures to Buzz, and I have to build another set of followers from scratch.
I'll continue to play with it, but I'm sceptical so far.