Here is a pertinent wikipedia article with some links: http://en.wikipedia.org/wiki/Ego_depletion

It's interesting how this applies to more trivial things, like trying to keep yourself from laughing.

Would it be a stretch to say that this supports the idea that we should automate as much of our lives as possible? If I don't have to decide to put a certain amount of my paycheck in savings every time I get it, and it happens automatically, I could potentially reserve that energy for another decision-based task.