I would say the following in response to "you don't do anything on a radiology rotation": if you are an introvert, and you are content to sit in silence, not ask questions, and not get involved, then you are not going to impress anybody.
However, if you go into the rotation with the attitude of learning as much as you can, asking questions ONLY WHEN APPROPRIATE (don't be a pest, that will hurt), and getting involved with what is happening in the department, you can make an impression.
Get involved in the resident run conferences that happen within the department; try to get in on resident or attending exhibits/posters/clinical research (a bunch of that going on in the months before RSNA); help look stuff up when there is a question while reading at the board; offer to take care of phone calls to teams on the floor, or going up yourself to checkout patient records for clarification on indications; help move paperwork around...etc.
And for god-sake, don't be obnoxious. They are going to evaluate you not only on whether or not you can be a team player, but also if they can stand being in one place with you for an extended period of time.
And one last thing, do not think they are going to be impressed by you disagreeing or over-speaking a resident. I've had several fellow medical students do this and it is absolutely a death knell.
I really enjoyed my away rotation and it is going to be my number one choice for a program. You may not love the programs you visit, and that is just as useful as loving it, because you know you don't want to waste your time applying/interviewing there.
