My next door neighbor in undergrad was in NROTC. He was originally was med corp, but he ended up in submarine. I had thought about doing it for aviation, but I ended up not. Other than the early morning PT and the Thursday drills, it didn't seem like there was much more commitment. Oh, and you have to do summer cruise, which can be annoying because it means you really can't plan on taking too much vacation. I think for Marine option you end up going to Quantico over the summer, but I'm not sure. From what I heard, NROTC was much more serious and disciplined than AF or Army. And this was at U of Michigan.