Few random comments/observations:
1) We have grade non-disclosure so grades really don't matter
2) Some consulting firms (only thing I'm recruiting for) ask for undergrad GPA on the apps. Some ask if you get called back for second rounds
3) GMAT matters but not nearly as much as b school apps. Not even close to as much
Overall, from what I've seen, if you put in effort during the process, you will get an interview (I don't know anyone who put in lots of effort at a firm who didn't get an interview. Well, maybe 1 or 2 but its rare). After that, you can overcome a low GPA easily and a low GMAT fairly easily. If you kill your interview you'll get an offer even if those data points are weak. That said, if its a tie between you and the 3.6/770 kid, she is getting the offer.
Don't worry about it at all for now (and go to a school w/ grade non-disclosure)
That said, poor GPA, GMAT and a low PST score will make the battle at Mckinsey a bit harder.