Caps Lock is almost certainly the most useless function of my keyboard. This combined with the placement and size of the key make it perfect for rebinding.
I spend a lot of time in vim, so rather than restoring the Control key to its rightful glory, I opted to swap Escape and Caps Lock -- GNOME makes this very easy.
It's saved me quite a bit of unneeded motion, and has become such a habit that I found the need to do the same in Windows. KeyTweak is a great utility that works on the common versions, and can do much more elaborate remapping if you desire.
Now if I can just ween myself off of the arrow keys and start using HJKL consistently, I'll be set!