I have a user who we just upgraded her MS Outlook from XP to 2003. I guess in the XP version of Outlook, when she would go to File > Open Other Users Folders to open another user's inbox, it would open up in a new window. This would let her view both her inbox and the other user's inbox at the same time.
In the 2003 version, it doesn't create a new window when she opens another user's inbox. Instead, it replaces the view of her mailbox.
I know it seems petty, but this user would like to have other user's folders pop up in a new window.