Given that this is one of my hobby horses, I'm interested to see Renard Sexton at 538 reporting that British Prime Minister Gordon Brown is supporting a referendum on "Alternative Vote" -- that country's name for this system. The object according to Sexton is to make nice with the Liberal Democrats in case Labour could cobble together a majority in coalition with them after losing seats in the upcoming election.
The article reminded me how different politics are in a place where there are more than two functioning political parties and those parties, at least ostensibly, stand for discernible policy platforms. I get to see and practice IRV in what are called "non-partisan" elections that are usually intra-Democratic party affairs with occasional Green, left or anarchist outliers. At our scale, these contests remind me of high school -- winning personalities count for a lot, policy only secondarily, though there are lines some candidates can't cross in some areas, for example failure to support tenant rights.
In the British context, IRV could enable Liberal Democrats and regional parties to win more seats, at least theoretically. But Sexton explains one likely result that is the best argument I've ever heard for IRV:
That's the best argument I've heard yet for this voting method. Since somebody is going to win, we do want to default to the least evil. But wouldn't it be nice to be able to vote for someone we thought expressed our actual inclination toward government without risking thereby putting in the most evil?
Take a hypothetical local example. Suppose, yet again, we're faced with the loathsome Diane Feinstein running for Senate in 2012. And it is a tough year for Democrats and she has a real Republican challenger, so we have to decide whether to hold our noses and try to ensure she gets back in, or just skip voting. It would feel better to be able to vote for Bozo the Clown as number one and only then list DiFi. Now there's a good use for IRV.