I am a creature of habit. Once I get into a pattern, especially with keyboard keys (i.e. my sleep key went missing), it is very hard for me to break the habit and learn to do something else to achieve the same goal.  One pattern I have grown accustomed to is hitting the Mail key and having Outlook change the selected folder back to Inbox.  This has worked for all releases of Windows until Vista.  Starting with Vista, when I pressed the Mail key, a new Outlook window was created that was focused on Inbox. 

Ergh, that is so NOT what I want to happen.

Not only was I running Vista, I was also running Office 12, so I could not tell if it was the OS or the app that changed.  I quickly ruled out Office 12 by installing it on XP and seeing the behavior I was used to.  So off I went into the registry and compared the any key or value I could find that had "mail" in it (brute force can be a good solution sometimes :) ) and I finally found the key and value in question.  The key in question is HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\explorer\AppKey\15.  I found that on XP there is a value "RegisteredApp" : REG_SZ : "Mail", while on Vista there is a different value, "Association" : REG_SZ : "mailto". If I added the XP value and deleted the Vista value (I renamed it actually to make sure I could easily recover if I touched the wrong value), the Mail key reverted back to the pre Vista behavior.  Even better, no reboot was required since it appears that this key and value are used everytime you press the Mail key.

I don't know why the change was made, there was probably a good reason for it.  I'm just happy that I could get the old behavior ;).  I don't know if this key is officially documented anywhere either.  If it is not, this is by no means an effort to document it and it could very well disappear in the next service pack, so use at your own risk.  And by the way, 15 is the value for the lParam APPCOMMAND_LAUNCH_MAIL for the message WM_APPCOMMAND, which is the message that is generated when the Mail key is pressed (I am sure that is not a coincidence).