Outlook 2007 places sent items into the general Sent Items folder. If you are using multiple or shared mailboxes, this is not always waht you want. You want a sent e-mail to be placed into the Sent Items folder of that mailbox. Here is how to do it:
Add/change the registry key as a DWORD (or paste this line into a reg file):
[HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Preferences]
"DelegateSentItemsStyle"=dword:00000001