One of my first posts on TFS API I showed how to obtain TFS User List (TFS API Part 4: Get TFS User List (Mail, Sid, Account, Domain))m Couple of days ago I got a question how to perform the same thing on TFS 2010, This is very simple:
In TFS 2008 the global user group were called = "Team Foundation Valid Users".
In TFS 2010 the name of TFS global user group changed to = "Project Collection Valid Users".
Identity SIDS = gss.ReadIdentity(SearchFactor.AccountName, "Project Collection Valid Users", QueryMembership.Expanded);
So, all you need to do is change the name to "Project Collection Valid Users" and everything should work.