E85 does not get better gas mileage than regular gasoline, it gets the same or worse. The only benefit is the slightly cheaper price (Which no longer seems to be the case as it were this time last year) of E85 and the ability to say you are sticking it to the Middle East (Of Canada. Canada is the largest supplier of oil to the US in terms of quantity). Ethanol contains less energy than gasoline, thus requires that 15% carrier of gasoline.
Ethanol, LPG, LNG, all have been tried in cars, yet nothing is as efficient as good old, gasoline.