Voting, Pleasure, and the Brain:
In response to Jim's argument that people vote because they find it pleasurable, my co-blogger Ilya writes:
I am skeptical about Jim's suggestion that the benefit voters get from casting a ballot is like " like going to a movie or a football game." Movies and football games are entertaining and fun (at least to fans). Voting is not. Very few people regularly choose to stand in line or fill out forms as a leisure activity.
  I wonder if the insights from Daniel Gilbert's terrific book, Stumbling on Happiness, might be helpful here. Gilbert, a psychology professor at Harvard, points out that our brains measure happiness differently when dealing with events that are far away in time as compared to events that are near in time. When an event is far away, we tend to ignore the practical consequences of it and instead latch on to a very incomplete vision of what the event may be like. So if a co-worker says, "do you want to go to Vegas with me 6 months from now?," you might be happy to accept because the abstract mental image of going to Vegas seems great. It's not until the trip is around the corner that you realize that the trip will be expensive, you have other things to do, you don't necessarily want to spend time with your co-worker, and the like.

  Applying this idea to voting, it suggests to me that Jim may be right about why people vote even if Ilya is right that people don't like to wait in line and fill out forms. When people think about voting in the abstract, they focus on the rush of it; the feeling of participating, of taking responsibility, and the excitement of not knowing who is going to win. Sure, they don't like to wait in line and fill out forms. But when they decide to vote they aren't thinking about that, just like they aren't thinking about what a pain it is to go to Vegas when the trip is six months away. And because voting is a repeated activity, the far-away vision tends to dominate the near-term vision. Looking back on it, people are glad that they voted in past elections because they remember the rush and the feeling of responsibility; the length of the line and the time filling out forms is quickly forgotten.

  Obviously this doesn't explain all of why people vote (or don't), but I think it suggests that the question isn't answered simply by a measure of objective costs and benefits; how the brain imagines future events seems to play an important role.