Microsoft Outlook 2010 introduced several new features.  Unfortunately, it removed one feature that many organizations utilize: sent items & deleted items support for shared mailboxes.  By default, Outlook 2010 will place all sent items and deleted items in the user's mailbox.  The issue with this is that users of a shared mailbox cannot see what emails have been sent out or deleted.  In Outlook 2007, you could manually enable this feature by adding a registry key.  This doesn't work the same way in Outlook 2010.  There is a fix though.

1. Obtain the hotfix from Microsoft found at http://support.microsoft.com/kb/2459115
   You need will need to fill out the information to have Microsoft send you a link to the hotfixes.  There is one for x64 and x86.
2. Install the provided hotfix.
3. On the client computer logged in as the user, add the following registry key (based on http://support.microsoft.com/kb/972148):
   
   [HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Preferences]
   "DelegateSentItemsStyle "=dword:00000001
4. In the mail profile, add each shared mailbox as an account.
5. Reboot the computer.