The first wave of Windows Server 8 documentation is available online:
There’s quite a bit of it. Couple of notable points:
- AD FS 2.1 is a server role. Features and functionality are the same as AD FS 2.0 but it’s managed via Server Manager.
- AD DS has loads of stuff worth reading about. But I’m most excited about the
claims based access control (CBAC)dynamic access control stuff.
Anyway. Happy reading! 
Hybrid Identity 