Google is launching an authentication (Auth) service that will allow third-party applications to better integrate with Google services. Nathan Torkington of O'Reilly reported this in their blog. So now you can allow a third-party application to access Google services on your behalf. Current limitations include having to manage separate tokens for each Google service. Google is looking into building a true Single Sign-on functionality in coming months.
This Google Auth service is limited to accessing Google services but with Microsoft trying to be a dominating player in the identity market it will not surprise me if Google over time builds out a competing offering to InfoCard (See Kim Cameron's Identity Blog).
I am personally interested in this and will post further- given my day job involves Identity Management.