I have 2 users who are getting enormous amounts of sync issues in their outlook. These users have large accounts and 4-6 other accounts mapped in the folder view. They will experience issues with outlook not automatically updating to show new mail. They either have to exit or click send/.receive. I have blown away and recreated their profiles multiple times. it fixes the issue for a few days but they revert back to the same problem after awhile. The sync issue they get says something about the system administrator setting a limit on the number of items open at the same time.
We run outlook 2007 on exchange 2007.