I'm going into neurology, and I wound up doing two aways: one at my dream program, and one at a very well-known big name program in a city where I had some friends, just for fun, that I had no intention of applying to. My dream program ended up losing some of its luster and moving way down my rank list, and I'm still not applying to the big-name one, but I learned a ton about neurology and even better learned about what sorts of things I want in a residency.
Audition rotations are a great idea and seem to be almost required in some specilaties (e.g. ortho), but don't limit yourself to doing away rotations only for the purpose of being a better residency candidate. I found out pretty quickly on the interview trail that by the time you get invited for an interview, the only thing you can do to really help out your candidacy is just be yourself, let your personality show through, and find the best fit for yourself. That said, doing an away rotation at a place is a great way to guarantee that you'll get a courtesy interview.
