Actually its in the form of E85 (85% ethanol 15% gasoline). Its been getting more popular in the midwest and any car that is flex-fuel can run it. Its really not a gimmick, but cars that are not optimized for it will generally get 3-4mpg less (although the fuel is about $0.60 cheaper a gallon so it makes up for the difference). The benefits are that it is a much cleaner fuel, both for the environment and your engine (less carbon deposits). And in the case of high performance cars, it can be used as a race fuel substitute because of its high octane and heat of vaporization.
Some people tune their subarus to run E85 all the time. But if they want to run gasoline again they need to reflash their ECU back to a gasoline tune. That's why I am integrating a flex fuel (ethanol) sensor so the ECU will automatically compensate for the amount of ethanol that is in the fuel tank.
Ive been looking at the lm2917 or lm2907, it looks like a simple IC to use. Based on the fact that I want a 0v-5v output would it be better to use 12v for the Vcc or 5v? Also what would you guys recommend for R1 and C1 values?