Statistically speaking, no single vote makes a difference in any election of reasonable size. I challenge everyone to try it: next election, don't vote. Then go back and look at the results. I'd be willing to bet that if you added your vote to either side of the election, it would not make a difference. This is especially true of State and Federal elections.
If that isn't enough, it might interest you to know that there is no fair outcome in these elections. This was proven mathematically by Kevin Arrow in 1951: http://en.wikipedia.org/wiki/Arrow's_impossibility_theorem
And furthermore, although I do not view the act of voting as explicitly immoral, any system by which a majority can force a minority to act against their will, without having initiated violence or the threat thereof, is clearly immoral. It ought to make one feel dirty to participate in such an act, seemingly (if not actually) legitimizing an immoral system-- Endorsing the idea that if their neighbors disagree with them on a policy, they want to see them forced to support it, by threat of violence or imprisonment if necessary.
So my question to everyone who votes is this: Why do you vote?
My suggestion to you is: don't waste your time.