Provide out of box support for Identity Federation using ACS. Justin Smit already posted a sample "ACS integration with Windows Live ID & Facebook Connect" on his blog and ServerSideWebIdentities.zip is also available for download.

AppFabric team should generilize this sample and expose endpoints like FaceBookFederation.aspx, GoogleFederation.aspx, MicrosoftActiveDirectoryFederation.aspx right inside AppFabric, not as a sample.