Ubuntu users (and possibly other GNOME users): Has your numpad randomly stopped working? This has happened to me, and a number of other Ubuntu users. It's really easy to fix.
Go to System -> Preferences -> Keyboard. That should bring up the keyboard preferences window. Click on 'Mouse Keys' tab. Disable the 'Allow to control the pointer using the keyboard' checkbox. Close the window. Also - Make sure Num Lock is on. Your numpad should now actually type numbers instead of move the cursor around.