The small enter key on older MacBook Pros is completely useless. Newer MacBook Pros have an option (Alt) key there instead which makes more sense.
With KeyRemap4MacBook you can remap many keys. It has a static list of possible key remappings which you can choose from, but they seem to cover a lot of use cases, You can also remap the eject key (which si also useless) as 'Del' (forward delete), but this does not work well for me as this key still has the delay and no key repeat.
Anyway, having a second option key is great and reason enough to install this: