re-read amcas, download research papers from labs I was interested in (not very useful, but I didn't have an MD or PhD interviewer), looked up my interviewer on the web, read medical ethics/health policy books
What impressed you positively?
Nice people and great school.
What impressed you negatively?
Lack of diversity in student population in terms of experiences, age, and interests. (I don't have a complete picture, but it seems to be mostly 22 year old white asians with no time off in between. There are exceptions, but they are exceptional.)
St. Louis--ouch! Not sure I can live there.