Wash U is pretty low key from the Adcom but I found that the other interviewees were the most stressful part. They were all Harvard and Yale types and me the only 'small liberal arts' school. One girl was on her 13th interview. The most stressful part of the interview day was that they expect you to find your way around the whole hospital by yourself and its HUGE! and I have a terrible sense of direction. I made it though.
They also have a pizza dinner thing the night before which I reccomend. It was good to relax and talk with other applicants in a more casual way than interview day. I don't recomend the dorms to stay in though. Or at least be warned that the are dark and depressing with community bathrooms. I was kept up for hours with the AIM pinging noise.
Good luck!