Using Azure Access Control Services we can leverage Facebook, LiveIDs, Yahoo and Google as well as public and private federations to log into SharePoint.  The best part is we can do with with requiring code.  The video below shows a demostration of using Facebook as a sharePoint login.  This demostration also shows how if we do want to extend the security model to secure SharePoint content by Facebook Groups we can do that by leveraging a Custom SharePoint Claim Provider.