Although the car is completely flex-fuel so that any proportion of ethanol/gasoline can be used, the mileage is less when running on E85. The engine gets 48mpg on gasoline and 37mpg on E85, however the gasoline fueled engine does not perform as well as the ethanol fueled engine. The cherry that tops off this desert is the fact that GM and Saab didn't stop there -- they installed a state-of-the-art hybrid system to combine the flex-fuel, turbocharged awesomeness with the added benefits of the hybrid technology. This is exactly the kind of innovative technology that is needed to put a dent in oil consumption and GHG emissions. With these two systems combined, car performance doesn't need to be sacrificed (like we see in those stupid European one-seater cars that look barely safer than driving one of my old micro machines on the interstate), and the gasoline displacement would be significant. Not to mention the amazingly high fuel economy even while running on ethanol and it is definitely a car for the next generation.
This type of car is still a few years off but the ideas are great. GM and Saab added that they aren't stopping at this concept car -- turbo downsizing, cooled EGR, and cam phasing are all indicated as techniques to lower emissions and raise mileage in the ethanol fueled car. This could lead to a truly E85 car that boasts lower emissions and increased mileage over gasoline. All-in-all, this type of story should be a huge boost of confidence for the innovation that will be coming down the pipeline in the next few years.