An interesting article up on Lifehacker about willpower studies done in the 1960s (presumably back when you could do this sort of thing) where researchers told children they could only have two marshmallows from a bowl and left them alone to see how long it would take before they ate more than two.
I think the problem with this study (for me), is that I don't really like marshmallows all that much (nor have I ever). So, I wonder if some of the children who successfully didn't eat more than two were like me. Anyway, very interesting stuff that talks about how willpower is often about distraction:
http://lifehacker.com/5216129/learn-willpower-techniques-from-the-marshmallow-test