I map esc to the key between left shift and Z. It doesn't exist on US keyboards, though. And I put backspace on caps-lock. What I don't understand is putting any kind of simultaneous combo key on caps-lock, since caps-lock + a is not really easy to press. It doesn't help that many keyboards have a bit of a gap between a and caps-lock (to help position the left hand and prevent accidental caps-locking?).