I have wondered whether there is any risk in doing an away rotation. For example, let's say I originally want to go to institution A for residency, and I do an away rotation. Then, if I decide during residency interviews that I love institution B and want to go there, could it hurt me? Would institution B rank me lower b/c I rotated somewhere else, on the assumption that I'm hoping to go there? I guess, you should just be prepared to explain to other programs you interview with why you chose institution A and whether you are totally committed to them or not.
I didn't do any away rotations, but then, I really had no idea where I wanted to go for residency when I was doing my scheduling in 3rd year. I ended up doing 3 one-month rotations in my 4th year at my school - surg path, heme path, and autopsy.