If you haven't seen this yet. It's worth watching to get a view on how Google plans to tackle the social graph opportunity. This coupled with OpenSocial could be a strong counter attack to Facebook:
Google engineer Brad Fitzpatrick gives an introduction to the Social Graph API. The Social Graph API makes information about the public connections between people more easily available. Developers can query this public information to offer their users dramatically streamlined "add friends" functionality and other useful features.