My school's premedical committee has us provide them with grades / mcat, a personal statement, an essay about shadowing experience, list of work / volunteer experiences, list any books / papers read that have to do with medicine etc. We then have two one-on-one interviews followed by a committee interview. They then write up an evaluation / recommendation letter based on all of these things. The evaluation was written by people who did not know me before the application process.
This committee application was very similar to a medical school application, which is a good and a bad thing. One of my interviewers commented that my committee letter looked just like one of their applicant evaluations that they wrote up after interviews and that it didn't really tell them anything that wasn't already on my application. It just confirmed what I had already said. Schools take evaluations like this very seriously from what I have been told, but it is good to augment this with a more personal letter from someone that you have had a relationship with. I sent in a letter from my PI with mine.