Here in Oregon, where I live, voting is done entirely by mail. The ballots, secrecy envelopes and return envelopes are mailed to all registered voters a few weeks in advance of Election Day. You vote from the comfort of your home and mail back your completed ballot (or you can drop it off at a collection location if you don't want to pay for the stamp). I just filled out my ballot and for the first time ever, I voted for a third party candidate for President of the United States.
My general voting heuristic has been to vote for divided government. (This law review article has had a lot of influence on my thinking, in that it argues persuasively that modern political parties have largely nullified the original conception of separation of powers; when Congress and the White House are in the hands of the same party, the checks and balances don't operate the way they should.) Admittedly, I don't always follow that rule. In 2008, for example, divided government would have meant voting for McCain, but I couldn't actually bring myself to vote for a ticket with Sarah Palin for vice president.
In any event, this year, the divided government rule doesn't yield an obvious choice, because it looks like the Republicans will hold on to the House, while the Democrats will hold on to the Senate. I suppose that if one party takes control of both houses, it's more likely to be the Republicans, but split control of Congress is far more likely.
Anyway, it just happened that this year, there was a third party candidate whose positions appealed quite broadly to me. Not all of them, but my views are idiosyncratic enough that it would be impossible to vote for someone who shared all of my views unless I were to write myself in. I've done that before, actually (I'm not in any party, so I wasn't a third party candidate), but this year there seemed to be no need.
I've had friends implore me not to "throw away my vote," but I don't see it that way. In terms of affecting the outcome of the presidential election, the chance is pretty much zero that mine will be the deciding vote. This is even more so when you factor in the Electoral College -- I live in Oregon, which Nate Silver currently rates as a 99 percent chance of going for President Obama. Put another way, if the President is at risk of losing Oregon's seven electoral votes because I vote for a third party candidate, he's going to get crushed in this election. Thus, my friends can point to the example of Florida in 2000 (when Ralph Nader got more votes than the difference between Al Gore and George W. Bush) all they want, but the simple response is that Oregon in 2012 is not Florida in 2000.
But what, then, is to be gained by voting for a third party candidate who stands even less of a chance than Mitt Romney does of winning Oregon's electoral votes? Well, I see the act of voting as being more than the binary choice of the Democratic candidate or the Republican one. There is an expressive component to voting that goes beyond the role that the vote plays in selecting the winner.
One can debate whether Nader voters in 2000 made a wise choice to support him over, presumably, Gore in a tight election. But Gore wasn't entitled to the support of those voters; he needed to earn those votes and for whatever reason, he didn't. Message sent.
To put it another way, a vote for a major party candidate counts the same whether it's an affirmative, enthusiastic vote for that candidate; an impassioned vote against the other candidate; or a lukewarm vote for whoever is perceived to be the lesser of two evils. The third kind of vote is perfectly understandable in a tight election in a battleground state, but message of discontent isn't likely to get through. A third party vote, on the other hand, sends a stronger message of discontent. If enough people vote for third party candidates, then the winner of the election can well find himself (or herself, in a future election) with less than 50 percent of the popular vote, as has happened numerous times, and therefore much less of a claim to any sort of mandate. It's "You weren't as lame as the other candidate" rather than "We like you, we really like you."
Life is short. If my vote isn't going to matter, then I'm going to vote my conscience.