[RKDinOKC]

Hmmm.

Make sure the calendar does not have any permissions set for the user in question.
Make sure the user that is getting corrupted does not have too many shared calendars open.
Oh and make sure they are using the scheduling assistant instead of opening the other user's calendar. Probably too many other users calendars open.
Not only create a NEW profile for the user with corrupted profile, but make sure old profile data files and autodiscover files are deleted from the user's computer.
If happens again, create new profile, export all data etc from Outlook. Delete user on exchange, create new user, add outlook, import data from backup.
If still gets corrupted, fire the user, or give them a new name a let them start over as another person entirely.

2. Have a user with permission to another users calendar with that other user's calender open in Outlook. Then give the user full access to the other users account. See what happens with the user starts getting double listings that will not open because they don't have permission.

See just how many email folders/messages a user can set up in their inbox.

See how may emails they can get in the sent items before it causes problems. Over 7,000 makes Mac Outlook delete and new sent items.