I completed a Doris Duke fellowship last year, had a fantastic time, and would highly recommend taking a research year to medical students interested in research. I took a bunch of coursework on clinical research design/analysis and worked on some clinical projects, but I spent most of my time at the bench. The biggest benefit I got was meeting a ton of inquisitive people and regularly discussing what they were working on, why they did it, and what challenges they were facing--I think I now have a better idea how people ask and answer interesting questions. On top of that, I got to live far from home for the first time (turns out life outside of California can be great) and was fortunate to make some really good friends. Time will tell how much completing a fellowship influences my match prospects, but I don't think it could possibly hurt me, and at least for me, the experience itself was worth the time.