If you are using vim a lot, and touch type, you may find reaching up to press escape all the time ruins your typing.
You can rebind escape to caps lock, and vice versa, throughout all your X apps using
Use this in
clear Lock keycode 9 = Caps_Lock keycode 0x42 = Escape
And then use the command, probably in your
xmodmap ~/.Xmodmap to do the rebind.