When you login, and use the wrong password, a modal dialog pops up telling you that you're an idiot. If you press Enter, it submits your wrong password again, and shows you the same dialog again. As far as I know, you must use the mouse to dismiss the dialog, then re-enter your password.
It would make me unreasonably happy if pressing enter would clear the dialog, and highlight your password.
Yes, I know this is immensely autistic, but hopefully it's also a quick change. :D