Suddenly after about half a year I wasn’t able to use my numeric keyboard anymore. And I use it. A lot. So, thanks to google and Nanci (http://nancib.wordpress.com/2008/03/17/fixing-the-borked-numeric-keypad-in-ubuntu-hardy/):
“Go into the Keyboard Preferences (System >Preferences > Keyboard) and go to the Mouse Keys tab. Simply uncheck the box for Allow to control the pointer using the keyboard.”