Yesterday Google announced it’s support for OpenID 2.0 protocol. So now with your existing Google account you can login and use other sites. I think this move was made after Microsoft announcing that they will give an OpenID for all its Windows Live users. This new log-in offering is not available to all site owners. But you can apply for it using the sign-up form. Zoho, Plaxo and Buxfer are the launch partners for this new API.
Google’s OpenID implementation doesn’t directly give your OpenID identifier to other sites, instead it acts as a middleman, authorizing you through it before it hands it over. Now a wide range of largest web service providers like Google, Yahoo, Microsoft, MySpace etc are using OpenID.
Google had announced that it is planning to combine the OAuth and OpenID protocol so that a service can not only request a user’s identity through OpenID, but also “request access to information available via OAuth-enabled APIs such as Google Data APIs as well as standard data formats such as Portable Contacts and OpenSocial REST APIs.”