He's modded Funny, but he has a point.
Escape -- because Alt+* is often grabbed before it gets to Emacs, I have to use Escape for Meta (so, yeah, Emacs user here). Plus it closes dialogs.
Caps Lock -- because I don't run Windows and don't have to rely on Word's autocorrect to enter uppercase letters with accents. My locale requires uppercase letters to retain their accents. CapsLock+é gives me "É" while Shift+é would give me "2".
Windows Key -- what, you never use Super on any keybinding ?
Scroll Lock -- console, 'nuff said.
That key that opens the context menu -- it opens the main Sawfish menu for me.
F-Lock -- I don't know what that is. Function-lock, for laptops ? I wish mine had that. Can't get used to hjkl for moving around in NetHack.
Pause/Break -- Free custom keybinding, hooray !
One of the Media keys -- I don't have a lot of those. Home, Eject, Previous, Stop, Play/Pause, Next, and volume control are all used (though Stop is bound to "show me what is playing right now".
So I guess I'd say Pause is the *least useful* after all.
Some of my readers ask me what a "Serial Port" is. The answer is: I don't know. Is it some kind of wine you have with breakfast?