People frequently say this sort of thing, but it's so rare for me to want to move precisely one line up--more usually, I want to move N lines up and M characters over. By the time I've mashed the arrow keys (or hjkl) enough to get there, I could have just as easily grabbed the mouse. Of course editors like vi and emacs have much more powerful movement capabilities, but those aren't "classic left-down-up-right".

What I'd probably most appreciate in Acme is a shortcut equivalent to / in vi, for those situations where I can see a bit of text I want to get to and it'd just be faster to hit (hypothetically) Ctrl-J and type a few characters vs grabbing the mouse. But I don't miss it often enough to go hacking the source :)