Being someone with a bad gpa/good mcat myself, I think there are two different types of people in this category.
Type 1: The die-hard partyers who spend half of their college experience with a BAC > 0.08, and imho adcoms tend to look at these people as lazy (ie: why didn't they just study? they had the ability to do well)
Type 2: Die-hard nerds who want to learn everything about everything/get over extended in EC's, to the detriment of their coursework.
Yes, type 2 people do exist. I would say that I was 90% type 2, 10% type 1. Ever since I can remember, I wanted to learn everything about everything. This meant watching TLC until my eyeballs were bloodshot, and reading practically all the science magazines I could find. When I was an undergrad, I wanted to learn everything about the UNIX computer system/Linux, and despite being a chem major, I spent 20-30 hours a week tweaking my linux box/recompiling my kernel. I learned a hell of alot about unix, and wrote a bunch of perl scripts, one to keep track of how much I was logged on: 15% of my time, or 25 hours per week. Everything about Unix was fascinating to me, and I spent alot of time learning as much about it as I could (and my grades suffered)
I was also taking way too much academically: I remember one semester where I was taking 5 classes, (4 of them science), and one of them was a graduate level molecular spectroscopy class that required graduate level quantum chemistry as a prereq. Of course I hadn't taken that yet, so I decided I would just learn it on the side
Plus I was doing Army ROTC 20 hours a week, and working 10 more hours a week. The point being, I was overextended, but I was also immature, irresponsible, and could not prioritize.
So as not to bore you with too many details, I'll stop here, but I think that if the adcoms had diagnosed me with "Type 1 GPA/MCAT discrepancy" I would have been in a world of hurt, but since my letters of rec, and my interview indicated "Type 2 GPA/MCAT discrepancy" the adcoms cut me a little more slack. I still had to prove myself academically, which is what I have been doing for the past 5 years: taking postbac classes, doing research (4 listed publications, 3 posters), and being an Army officer in the National Guard. However, after 3 long years of applying, I finally convinced them that I was a different person than when I was an undergrad 6 years ago, and as a result, I now have a couple of acceptances.
GPA: 2.5 undergrad (MIT), 2.78 AMCAS with a strong upward trend
Postbac, while working fulltime: 2 B+'s (1 in grad bio), 1 A- (grad bio), 3 A's, 1 A+.
MCAT: 10V, 13P, 14B, R
-ttac
