[sirsean]

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.

[mcaruso]

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.

[jensnockert]

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.