As a proud, new (two weeks) owner, my wife and I went through the various rationalizations necessary to buy a new vehicle which, for the EXT, included gas mileage.
My math went something like: 10,000 miles/year @ 15mpg @ $3.00/gal. (not there yet, but we know it's gonna be there and beyond eventually) versus something else that might get 22mpg. The difference in this case is $53 extra per month to drive the Escalade. For us, it was well worth it, though our friends who drive a 40mpg Prius just shake their heads in wonderment...
Our last two tanks have averaged 18.2 including several high Rocky Mountain passes and 75-80mph highway driving, but only a little around the city.
Ooh, my first post...that wasn't so bad, was it?