Steven Levitt (of "Freakonomics" fame) has a little video on the NY Times' web site explaining why economists don't vote. First, the fact that economists don't vote is news to me, I cannot think of a single example of a colleague who doesn't vote as a principle, and most of my colleagues in the departments of which I have been a part have all voted en-masse. Second, Levitt's explanation for this behavior (which I don't observe) is a familiar one in economics: that the marginal impact of one single vote is zero so there is no reason to vote given its non-zero cost. Now, of course, if you have been well-conditioned and believe in your civic duty to vote you may get utility from doing so, which may explain why some people vote, but in general it does not make sense for most people to vote. Economists, wise as they are, understand this and so don't vote. QED
But I find fault with this reasoning. It may be true that my vote is insignificant, but I believe in markets. And voting on a candidate, measure, etc. is a way of allowing the 'market' to decide on an idea or set of ideas. The only way for this outcome to be efficient is for there to be mass participation in this market and I understand that, while I may be mostly insignificant, I play an important role in making the market efficient. And I, like most economists, believe in efficiency. So I think economists believe in as much information and participation as possible in an election and thus understand that we all do have a small but significant role to play.
Oh and by the way, voting on blog polls is an entrely different matter - your vote is crucial to the well being of all humanity, so make haste and vote!