I'm finding it a bit annoying that it's difficult to see which pane one's editing. I wonder if Jon would dream up a nice way to make it clear.
One possibility would be a block cursor option, combined with the various blinking styles I think this would be very nice. It's also far more visible than the thin caret or underline cursor, and would help toward seeing "where you are". Heck, I'd love a block cursor anyway, but I am regularly losing which pane I'm editing, especially when alt+tabbing away and back; it's annoying me more and more lately.
ps. I know there are some plugins that attempt a block cursor, but I think a "proper" native cursor would be a better option all round.