One of my clients is a state government agency with branch offices that share office space with other agencies. All the agencies want to share free/busy data for shared resources such as conference rooms, but they don't want to synchronize their entire directories. Do you have any suggestions?
The agencies can use the InterOrg Synchronization Tool to synchronize the Schedule+ Free/Busy public folders among organizations. (You don't specify which version of Exchange the agencies are using, but "Exchange Server 5.5 Interorganizational Solutions" August 2000, InstantDoc ID 9135, provides additional information about using the InterOrg Synchronization Tool.) The process is well understood and mature, but the replicated free/busy data will be meaningless unless each side has some way to see the resource objects from the other side. In other words, you need to implement some degree of directory synchronization for the solution to work. If you can convince the agencies to put their resources into a separate organizational unit (OU), you can use the Microsoft Identity Integration Server (MIIS) 2003 Identity Integration Feature Pack (IIFP) to synchronize only those OUs.
The bigger question is whether these agencies—or any set of organizations in a similar situation—should be synchronizing directories at all. A centrally maintained directory for all agencies is a better solution. (Good luck pushing that through!)