One of my customers was using Outlook Web Access on their Windows Mobile device and they were caching the password on the device.  They had a problem that when their Active Directory password changed there was no way to reset or clear the password outside of doing a hard reset on the device.

Well we figured out a solution.  If you get a registry editor and go to:

HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Passwords

You should find a key name the same as your corporate OWA server.  If you delete the key and then try and access OWA again you will be prompted for the new password!