XFire's default key combination to open conversations up in-game is Scroll Lock + X, that's the only time I use Scroll Lock.
I never use Caps Lock, I always forget and just hold down shift with my right pinky (only type with my index finger with the right hand)
The key that would have to be the most useless of them all is Pause/Break, I was actually looking at my keyboard the other day and thought to myself, my god, I have found a key on keyboards that I have never used and have no idea about.
Insert is pretty silly too, I used to hit it sometimes and then be enraged when unable to type if I go back in text to fix something.
Windows keys aren't remapped or taken out, I don't know any shortcuts either, since mechanical I haven't had any accidental windows key presses.
Another key I've been wondering about is the key between the right windows key and control, is it called Menu? I have never used that and think it to be pointless.