I generally run Linux. I use Vim a lot, so the Escape key is extremely important. I also use other keyboard shortcuts a lot, so Control is "key" as well. On Linux, I've solved this by using xcape to map the Caps lock key to Escape if pressed by itself, or Control if pressed in combination with another key. This puts the best of both worlds within quick reach of my pinky finger. Is there any way I can do this on a Mac?
First, go into the Keyboard preference pane, click "Modifier Keys…", and change Caps Lock to Control. Then, go into KeyRemap4MacBook and search for this option:
Check that, and you're done. With KeyRemap4MacBook you can do lots more interesting things, like mapping your (now kind of useless) Escape key to a Hyper key with even more keybindings.