Stanford Report has a university public press release about a recent paper [subscription required] in Psychological Science.  The paper is available for free from a website of one of the authors.

The gist is that they find evidence against the (currently fashionable) hypothesis that willpower is an expendable resource.  Here is the leader:

Veronika Job, Carol S. Dweck, and Gregory M. Walton
Stanford University

Abstract:

Much recent research suggests that willpower—the capacity to exert self-control—is a limited resource that is depleted after exertion. We propose that whether depletion takes place or not depends on a person’s belief about whether willpower is a limited resource. Study 1 found that individual differences in lay theories about willpower moderate ego-depletion effects: People who viewed the capacity for self-control as not limited did not show diminished self-control after a depleting experience. Study 2 replicated the effect, manipulating lay theories about willpower. Study 3 addressed questions about the mechanism underlying the effect. Study 4, a longitudinal field study, found that theories about willpower predict change in eating behavior, procrastination, and self-regulated goal striving in depleting circumstances. Taken together, the findings suggest that reduced self-control after a depleting task or during demanding periods may reflect people’s beliefs about the availability of willpower rather than true resource depletion.

(HT: Brashman, as posted on HackerNews.)