Hi,
Here's my two cents... I had heard similar things about differences in residency practice throughout the U.S. I was planning to apply to programs that were not just in my region and so decided that, for me, doing an away rotation would give me the most information possible and help me be more informed when I was eventually interviewing and making my List.
I ended up doing an away rotation and was really glad that I did.
There are two schools of thought on away rotations, however. Some people say that they will most likely hurt you rather than help your chances for residency. There is some truth to the idea that if you happen to not gel personality-wise with the rest of your team, you may be much less likely to get an interview. Even if the rest of your application is stellar, if individual residents/attendings decide they don't like you it would likely affect how the rest of the Committee sees you & ranks you. Alternately, if your application is not so stellar, an away rotation may help you prove that you actually know what you're doing.
Most people say to try to do a Sub-I in the summer so that you can get letters of recommendation for your application. Whether you do that at your home institution or away (or both) is your call. I think trying to do a Sub-I at least by November is a good idea.
Most schools have easy links from their main medical school webpages (or from a "Curriculum" page) about how to apply to be a visiting student. It would probably be a good idea to start browsing those pages soon, because the deadlines really vary from school to school.
Good luck!
