If you live in Georgia, California, or Texas, Obamney will either win or lose the presidency with or without your vote. If you really want to help your Republocrat of choice, call up a friend or family member in Colorado, Ohio, Florida, Virginia, Iowa, or North Carolina, where one changed vote (or someone you convince to vote who wasn't going to) has the same impact as a dozen votes in your state (your vote and the vote of ten of your friends).
How can this be the case? Each vote has a probability of influencing an election and a voting bloc of a hundred votes is approximately a hundred times as likely to change a state than a single vote. However, with the electoral college, people who live in swing states have a voting power ten to a hundred times the voting power of someone living in a non-swing-state, because their vote lies on a different place on the bell curve, so to speak. (100 people voting blue in Texas might change the probability of going red from 99.99% to 99.98%, but change it from 63% to 62% if voting in North Carolina.)
You won't hear about this on the news, but I guarantee you that campaign strategists in both camps have calculated numbers for the relative importance of voters, and found that each vote in these swing states are at least ten times as valuable as your vote. Still, the illusion of democratic power is crucial, so it is imperative that you still vote.
Incidentally, here are the 6 crucial states, their electoral vote allocations, and their probability of swinging one way or the other, according to wonk statistician Nate Silver
Colorado (9 votes, 72% chance Obama)
Ohio (18, 82% Obama)
Florida (29, 67% Obama)
Virginia (13, 74% Obama)
Iowa (6, 77% Obama)
North Carolina (15, 65% Romney)
Romney basically needs five out of six of these states to win, when he's expected to get one out of six. If the election were held today, there would be at least a 90% chance Obama would win. Unless something drastic changes, Obama will continue his presidency through 2016.
I intend to vote for Gary Johnson in the coming election, and encourage you to do the same if his positions resonate more with you than the other two, regardless of whether you love or hate Obama (unless you happen to live in one of the above six states, in which your love or hatred can translate into tangible gains at the voting booth).