Something that I haven't heard much discussion about yet...

[rogerashton]

7. New ideas are tough to get across.

People have been thinking about how to run elections for about 200 years. Chevalier de Borda, late 1700's, was probably the first to propose that second and third choices, etc., might be taken into account. The instant runoff (single transferable vote) is a newer idea. Well, somewhat newer -- according to Wikipedia it dates to the 1800's.

http://en.wikipedia.org/wiki/Instant-runoff_voting

Why has it not been a part of our electoral system? Probably because those who are elected by the current system have some interest in keeping the current system. But breakthroughs do happen.

As to the pitfalls, I'm not the one to ask. But I will say this. No system is perfect. Any system of elections can be "gamed." That's not cynicism -- it is mathematics.

Gibbard, Alan (1973), “Manipulation of voting schemes: a general result,” Econometrica v. 41, no. 4 pp. 587-601.

But at least, with "instant-runoff" voting, people are not forced by circumstances either to game the system or to throw away their vote. But I repeat myself.