How about this particular issue with third party (Blackberry and Goodlink) wireless calendars?
http://support.microsoft.com/?id=899919
It seems to me that deleting a calendar item and recreating it will only cause confusion for any third party applications.
The cut over from using Entry IDs to Global Object IDs seems to be dependant on switching from Outlook 2003 SP1 to Outlook 2003 SP2. This feat is darn near impossible to coordinate in large organizations, and third party vendors will have a terrible time trying to figure out which field to key on.
In other words Microsoft is pretty much forcing third party vendors to code in for both situations simultaneously, otherwise organizations have to hold off deploying Exchange 2003 SP2 to try an deflect this problem.
This doesn't make sense to me...