There is a new technet article written by Michael Khalili, an Exchange PM, which talks about some of the ways that Exchange 2007 and Outlook 2007 play together better than their older relatives did.  The most exciting piece mentioned in this article for me, as an Outlook/Exchange developer, is the Calendaring piece.  Of all the APIs we support it seems to me that most of our questions and bugs center around calendaring, any improvements/simplifications in this area are very welcome.  Here is an excerpt from the article about prior problems with Free/Busy data...

"In the past, most calendar logic resided in Outlook. Each meeting update was treated as a separate meeting invitation, which meant the notifications could be accepted out of order. If two meeting updates were sent in quick succession, and a recipient accepted the second meeting update before the first, he might have out-of-date information on his calendar. Furthermore, accessing Outlook information from Smartphones or PDAs could lead to differing free/busy information according to the method by which users viewed the data."

...been there, done that...

"The solution was to move all calendar logic from the Outlook client to Exchange Server 2007.  When a meeting request is received by the server the meeting is automatically placed on the calendar as tentative until the user chooses to accept or decline the appointment. If a time or location change to the meeting is received, the meeting will be automatically updated and the old invitation marked out of date so users will not accidentally accept it. This logic is consistent among all clients—Office Outlook, Outlook Web Access, Outlook Mobile, or another third-party client—so only the correct, most up-to-date meetings are present."

...very nice.  As Outlook/Exchange developers we are dependant on the information returned from APIs (which in turn comes from the application's proprietary business logic) to present accurate information to the user in our applications.  The more Exchange understands or centralizes Outlook's business logic as it relates to calendaring, the more accurate that data, and therefore our applications become...