I heard that adding 2 onces of pure acetone to 10 gallons of gas will improve your gas milage. Is this true?
It sure will. It will increase it about 0.078125%.
It may clean some deposits, and it may damage some parts, but neither is likely. Modern gasoline comes will all the additives it needs. Stick with gasoline.
If you really want to improve your mileage, get a car with better mileage rating and even more important, keep your car properly maintained and drive for economy.