As mentioned on Sunday Google announced today Google Friend Connect.

Tonight at Campfire One Google will preview Google Friend Connect.

Visitors to any site using Google Friend Connect will be able to see, invite, and interact with new friends, or, using secure authorization APIs, with existing friends from social sites on the web, including Facebook, Google Talk, hi5, orkut, Plaxo, and more.
Google Friend Connect has been developed to lower two barriers to the spread of social features across the web. First, many website owners want to add features that enable their visitors to do things with their friends, but the technology and resource hurdles have been too high. Second, people are tiring of needing to create new logins and profiles and recreate their friends lists wherever they go on the web. Google Friend Connect offers a solution to both these issues.

Google Friend Connect is in a preview release, available tonight after Campfire One on a handful of whitelisted websites.
Via this Google announcement.