Positive. Our school releases all possible stats about medical school applicants. My undegrad also has mandatory pass/fail classes which cannot be taken for a grade (2 of my courses I was forced to take pass/fail).
Let's take a look at my transcript (an n=1 example).
Class taken pass/fail
1) Intro to Engineering (mandotary pass/fail)
2) Calc I (mandotary pass/fail)
3) Calc II (opted to take pass/fail)
4) Orgo I (opted to take pass/fail as I was NOT pre-med in college and this class had a bad reputation. I re-took this after I graduated and received an A- after college).
5) Globilization and Social Conflict (opted to take pass/fail as I thought the class would be interesting... regret taking this class as it was really, really boring and I didn't learn much).
6) Principles of Physiology (opted to take pass/fail. Re-took after graduation and received an A).
7) Animal Behavior (opted to take pass/fail). Took this class out of interest and really enjoyed it. I aced this class.
8) Principles of Neurobiology (opted to take pass/fail as it was required and I heard rumors the professor sucked). The professor sucked, but I aced this course and decided to focus in neuroscience.
9) Intro to Econ (opted to take pass/fail since it was senior year). Aced it since it was a freshman class and pretty easy.
Since I graduated I took one more class pass/fail.
10) Molecular bio. Opted pass/fail since I really just wanted a biology refresher for the MCAT.
NOTE: I was not pre-med during my college years. Had I been I would have opted to take bio classes and orgo for grades. Some schools don't accept pass/fail classes as pre-reqs so I had to spend money to re-take classes like orgo. In retrospect, I should have taken them for a grade as an ungraduate student, but you live and you learn.
Also, about half those classes would have probably been As. Neurobiology, animal behavior, physiology, econ, intro to calc I were all classes that I did well in but now appear just as passes on my transcript. I could really use the GPA boost that this would have given me. On the flip side, I did really poorly (but passed calc II). All of the classes that I re-took were over 5 yrs apart. I would definitely NOT re-take a class the following year since it's obvious you did poorly in it.
Edit: There are about 180 applicants per yr from my undergrad, so it's a similar sample size.
Really? Are you sure about this? I'm not saying whether your right or wrong, but this seems to be an incredibly high number. The average from my undergrad was probably less than 1 per 4 years (although there are approximately 150 applicants from my school per year, so the sample size could be widely different).