I'm hoping for GMATClub to do a more indepth analysis on its own data in the upcoming months (I don't have the bandwidth to do it myself). Businessweek, for quite a few schools, does gmat versus acceptence rates (unfortunately, a lot of the top 10 schools are missing).
But in general, GMAT matters a lot, although it does vary by school. Among the top 15, Cornell and Duke are the two that DON'T show a high correlation between GMAT and acceptance. UCLA, Yale and Stern on the otherhand shows an extremely high correlation between GMAT and GPA. Wharton and Booth show a high correlation between GMAT and acceptance too, but those have a bit of selection bias in who applies going on.
Heres 2 examples: go to more information, and entrance exams -
Duke:http://www.businessweek.com/bschools/ra ... fuqua.html
UCLA:http://www.businessweek.com/bschools/ra ... /ucla.html
You can see the big difference between the two. At UCLA, the acceptance rate effectively doubles from ~700 to ~750. Personally, I think the difference is even bigger than this for two reasons: A lot of the low GMAT acceptances are URM's. A lot of the high GMAT rejections are indian applications (which have a MUCH lower acceptance rate, and MUCH higher average GMAT at top schools). I'm hoping for a better analysis to come out, but if you're a white/asian American male, I think it's going to come out your chance of acceptance effectively triples from low 700's to mid 700's at many top schools.
You always need great work experience, and usually good undergrad performance, to get into a top school. But, if you're a competitive applicant bringing your score from 700/710 to 740/750 can DRASTICALLY increase your chance of acceptance. When I see consultants/people on forums say that once you break 700, you shouldn't take the GMAT again, they are completely missing whats happening in admissions. Admissions at most of these schools aren't nearly as "holistic" as they are made out to be. They are chasing rankings, and GMAT is important to rankings.
I really wish I had known which schools over and under weighted GMAT when applying. I wouldn't have applied to Duke if I had known - Duke ended up giving me a smaller scholarship than Kellogg, even though Kellogg is ranked better by quite a few spots. In general, schools with a below average GMAT for their rank under weight GMAT, and schools that have above average GMAT for their rank over weight GMAT. I made this mistake of thinking schools with lower GMAT's are "easier" to get into (relative to their rank), when it really just means they care less than other schools about GMAT.
P.S. Some schools actually break applications up, as their first step, by GMAT score, and put 730/740+ in separate piles (and below 700's in a separate pile).