I never use Caps Lock, so I disable the Caps Lock key completely with xmodmap, to avoid hitting it by accident.
Occasionally my X server gets into caps-lock state anyway. (Usually some complicated stunt was involved, like attaching x11vnc to the display remotely.) And then I can't turn it off again using the Caps Lock key.
So I wrote a tiny X client that lets me type 'xcapslock off' at a shell prompt …
… and then I had to make an alias to it, called 'XCAPSLOCK OFF'.
@simontatham I actually use and like to have Caps Lock.
But I believe the Debian installer still contains a change I made when I discovered that the Brazilian Portuguese keyboard layout has 106 keys, and / is on the 106th key - so I had to be able to switch out of it manually without needing to type any absolute paths!