One of the changes that might puzzle administrators new to Exchange Server 2007 is the move of the recipient management interface from Active Directory Users and Computers to the Exchange Management Shell. (Microsoft is actually reverting to the pre-2000 situation)
The exchange team provided a nice overview on how to complete most popular recipient management tasks using the new tools: How to do your top Exchange Server 2003 recipient tasks in Exchange Server 2007.
Those that absolutely want to keep doing their job from within the AD console might want to look into the solution proposed on msexchange.org. (3rd party solution).