I changed Caps Lock to Control, which is extremely helpful. Especially since on the Macbook keyboard, it's tough to reach down and hit the Control button without accidentally hitting Function instead.
Super annoying. Very first thing I did when I got my MacBook was install KeyRemap4MacBook (http://pqrs.org/macosx/keyremap4macbook) to switch Control and Fn.
I do the same, in addition I also use it to map caps lock to an unused key (F14 or something) and use it for changing input sources.