Word leaked out yesterday that Google was planning a new service for Gmail that essentially turned the popular Web-based email service into a rival to Facebook and Twitter. Now, we're finding out more details about the service, which has been dubbed Google Buzz.

"Google Buzz is a new way to start conversations about the things you find interesting. It's built right into Gmail, so you don't have to peck out an entirely new set of friends from scratch — it just works," the company writes in a blog post today. "If you think about it, there's always been a big social network underlying Gmail."

Microsoft was unimpressed. “Busy people don’t want another social network, what they want is the convenience of aggregation. We’ve done that," said Dharmesh Mehta, director of product management for Windows Live , in a statement. "Hotmail customers have benefitted from Microsoft working with Flickr, Facebook, Twitter and 75 other partners since 2008.”

Yahoo too says it beat Google to the punch through its Yahoo Updates service, with Alley Insider publishing an email from the company indicating that they see social networking tools as "an enabler and as a dimension that is part of everything we do -- and everything people do online."

Google Buzz connects users to the people they email and chat with most frequently, and allows people to integrate photos, videos and links with large or small groups of people. It also integrates with sites such as Flickr and Twitter, with Google noting that their goal is to make "Buzz a fully open and distributed platform for conversations."

Google started rolling out the service today, with plans to have it available to all Gmail users in the next few weeks. It also introduced Google Buzz for mobile devices allowing users to tag posts with geographical information.

In a way, the service reminded me a bit of Gist. The Seattle startup -- backed by Paul Allen and others -- says it helps users "build stronger relationships by connecting the inbox to the web." Last September, when Gist launched, CEO T.A. McCann said that users could choose what services (LinkedIn, Gmail, Outlook, Facebook, Twitter, etc) they wanted to set up in Gist.

You can see how Google Buzz works in this video.