capneedles mention there is the exact reason why people have the belief that doing a rotation is the key into getting into a program. It's not a cause and effect relationship, it's just a correlation. People rank their away rotations higher, and the programs usually rank the students higher. That's how it goes... so people think you need to ace the rotations in order to get into residency, which is not true (although you *should* work your ass off, but that's another story). You should keep in mind that the value of the away rotation is to get your feet wet, get some letters and contacts. If nothing else, it's something to talk about on your interview. I can't tell you how many times I have been asked where I rotated on interviews. I learned my lesson, I don't say anymore. I say oh, I rotated here in the northeast or *insert whatever region you're currently in*. Usually no one asks that.
Like for instance, I have been asked 'where else have you interviewed'. I don't list programs anymore, I say "oh, in NY, some in california.. anywhere, since matching is the most important".. that answers the quesiton, and I think in effect eliminates the possibilitiy of them judging you for your choice in rotation. Trust me on that one.