Definitely a great thread. I don't dispute the point made earlier that being an URM doesn't play a role in admitting individuals from the lower end of a school's 80% GMAT/GPA range. But I think the diversity at the lower end of this range is not just limited to ethnicity or gender but also career background, career goals, and life stories, etc.
I spent most of my life until now refusing to "check the box" because I would rather know that I got somewhere in my life because I was great at what I do not because of my heritage. I was OK with my grades, OK with my test scores my entire life but always was the leader of everything I did and received several awards all through HS and Undergrad.
I only check the box now because I had a conversation with an AdCom member from a top 10 B-school who articulated to me that they don't see the URM status as being more lenient but they want and need a diverse program. Whether I check the box or not, they're going to maintain a diverse program either way and I may fit into one of the other "boxes" that they're looking for (career background, career goals, and life stories, etc.) given my solid marketing/advertising background and desire to go into a non-traditional career in Media and Entertainment. The big thing I might be passing on by not checking the URM box is scholarship money. Which, given the prospect of paying for everything myself with no help, is a BIG reason for me to check the box.
I apologize for the long commentary but I say all of this to say, the numbers don't say everything and because I can check that box does not mean it's the only reason why they're going to admit me. I still need to be able to succeed in B-school and even more importantly, I need to get a job and be an advocate for the school when I'm done and give them lots of money

. If I wanted to go into I-Banking or Consulting at a top firm with my GMAT, they would probably laugh at me because the odds of me getting a job with my GMAT is slim to none.
My profile and link below have my full background.