You would think that your undergraduate GPA would be weighted more heavily, but at most schools it isn't — and for good reasons.
First, most B-school applicants weren't planning to apply to graduate programs, so they might not have focused on playing the grade game the way most premed or pre-law students did. Why hold mediocre grades against an applicant who had no intention of applying to grad school five years down the line?
Second, that was then and this is now. I've been told by many admissions officers that they discount undergraduate GPAs because they are old measures of performance. Admissions officers are more interested in how you perform now — thus the emphasis on GMAT scores.
I remember one director, however, pointing out how the emphasis on GPA can vary from candidate to candidate. He said that he has to rely more heavily on GPA when evaluating the candidacy of a relatively young applicant who has been in the workforce only a short time.
For another applicant with five years of work experience, however, he puts more emphasis on that experience and on the applicant's GMAT score, and less emphasis on his (distant) undergraduate GPA.
While I list GPA as number 4 in order of importance, you shouldn't think that its value is set in stone. The evaluation process is fairly holistic, so if you performed well in college, emphasize that performance and the admissions staff may buy into it. If you didn't perform well, talk about your terrific GMAT score and ignore your undergrad years.
Whatever you do, don't whine about your mediocre grades; take responsibility for them. There is one excuse, however, that you can always get away with. If you worked and paid your own way through undergrad, be sure to mention that in your essays. Working is the one universal justification for bad grades. (A comment I've heard from many admissions officers.)
While you might be able to explain away your less-than-stellar undergrad GPA by informing the admissions people of the Twinkies-and-beer lifestyle of your college years, you won't be able to slide bad math grades by them quite so easily. Admissions people will look closely at your undergraduate math performance.
As I mentioned in the GMAT section of this Web site, admissions officers are very concerned about math skills. If you believe that your math grades are not up to par and that your performance on the math portion of the GMAT isn't good enough to make up for those grades, do everything possible to take a math course through a local university before applying to B-school. You need to allay the admissions committee's fears about your ability to cut it in math-intensive classes. While you can be accepted into a great MBA program with only better-than-average verbal skills, you won't be accepted if you are suspected of having terrible math skills. So fix your math profile.
You can't change your GPA, so there isn't much sense in worrying about it. People with bad GPAs get into great schools all the time, though, because they have strong GMAT scores and great essays.
Don't let your GPA keep you from applying to top business school. The median GPAs reported by some top programs can be intimidating, but the GPAs of accepted students vary a great deal—even more than do their GMAT scores. (The middle 80 percent range at top schools can be 3.0 to 3.8.)
One thing you can do, however, to address your GPA is take some classes through a local university extension program. School is a lot easier the second time around, and you might be surprised to find that you can now get good grades in classes you used to hate. Performing well in school now should convince admissions officers that you can do well in their program regardless of your undergraduate performance.