in reply to The most useless key on my keyboard is:

Some of them are very useful, or can be turned to usefulness :)

PrtSc/Sys Req : kernel-level keyboard shortcuts
Caps Lock : remapped to Tab
The 'Windows' key : launch xterm
F12 : tty12 is the place for logs !
Esc : a Vim addict as I am can't live without this one !