Windows 8 Release Preview and Windows Server 2012 RC Compatibility Cookbook
You won't find any recipes in this cookbook, but what it does contain is details of new and depreciated features in Windows 8 and Server 2012, along with guidelines and best practices for developers to verify the compatibility of their applications.
There are also a few things that may be useful for network managers to know about such as howto install .NET Framework 3.5 without accessing Windows Update (p22), support for legacy DirectX 9 graphics cards (p78), file associations (p13) and booting from VHDs on SSDs (p107).
Download / Online Version
If you don't feel like reading through all 127 pages, there's a good summary here.