After 1800 miles I've been able to come to this conclusion. GM cars have a dual personality.
Bear with me on this explanation...
My Traverse is the 6th GM product I've purchase for myself in personal use. One thing I've always loved about the GMs, compared to the Toyotas, Hondas and a small Mitsubishi truck I've driven in the past is that when you want to move, they respond and respond with a good punch of speed. I'm a little put off by the accelerator lag of the Traverse, but that's another topic. But, after the gas is on the speed can really take you back. Other vehicles have similar 0 to 60 ratings, but their method is to speed up more gradually and power in later. I prefer the speed sooner. GM cars deliver it that way.
Now, the trade off for this as it seems to me is that if you want to be pedal heavy you'll pay the price in gas usage. My wife drives a lot more gentle than I do. She always gets noticably better gass milage than I do. She even pulled 24 MPG in the old V8 Chevy pickup I used to drive on one trip she made a few years back. I've noticed this with my Traverse. I've I drive (ehem...) like I should I get great milage. If I push the pedal to get that burst of speed a little too often, it drinks it in. I do get the return on my investment for the pedal pushing with that nice satisfying burst of speed. It's just a price to pay.
Anyway, that's my take on it. I still get better milage than my old truck in normal, sometimes pedal heavy, driving like I do day to day. So I'm not displeased at all.
As for numbers so far: I drive pure city on a day to day basis. My old truck got around 14 MPG, the Traverse has been getting around 15 MPG in this mode. I usually saw around 20 MPG in the truck on steady smooth highway driving @ 75 MPH, the Traverse I've been able to get just over 22 MPG.
As another example, my wife's HHR has a very nice powerful inline 4 with rated 22 city, 29 highway. She averages 24 MPG on her DIC with mixed driving. When I get behind the wheel of her HHR, I drive it down to 14 MPG quickly >

I can't keep my foot out of that little peppy 4 banger! LOL!