One of our clients uses a MacBook Pro for doing development work. She uses Microsoft Visual Studio on Windows XP running under a Parallels virtual machine. Today she managed to get the keyboard stuck in delete mode, instead of the standard insert mode. Typing new text would not move the remaining text to the right, but instead would go right over the top of the old text.
I did some research and found out that she uses the Ctrl+Shift+M keyboard shortcut a lot for some weird SQL thing and had accidently hit Fn+M. It turns out that Function M is the equivalent of hitting the Insert key on the numeric keypad on a standard full sized keyboard. Presto! Problem solved.