Now imagine congressional elections with STV, and no primaries. The candidate who appeals to many but not all Republicans, and also appeals to some Democrats, has an advantage over his fire-breathing opponent. And he should, since STV aggregates everyone's preferences, not just that of the plurality.
I've slowly grown to like the idea of using instant runoff (the term with which I was introduced to the concept way back in 11th grade) more and more. I should note that the local elections in November here in Minneapolis used IRV, and in the same elections, St Paul approved a referendum to hold future elections with the same method. First past the post voting like we have for national elections in the US basically locks third-party candidates out for fear of "wasting your vote". With IRV, you can vote for that third party candidate, but ensure that your vote counts for the mainstream candidate as well. Hell, if nothing else, Gore likely would have won in 2000. It certainly isn't the be-all, end-all of electoral reform, but hey, it would be a nice little start. Then work on campaign finance. Or just get to work on campaign finance now.