Brian Desmond understands how to run Active Directory successfully better than most folks and has thorough knowledge of how it works. Brian is a Microsoft MVP and has been exposed to the Windows 2008 Active Directory changes for over a year now and the product hasn't even hit the shelves yet!
Joe Richards is a consultant/admin/tool writer and Microsoft MVP for Windows Server Directory Services. Joe updated the second edition of Active Directory Cookbook for O'Reilly.