My brother and I used acetone for awhile. He saw a small increase in gas mileage, definitely not 2x, and he drove mostly on the highway from Kent to Columbus.
I, however, saw almost no increase in my gas mileage (a lot more stop and go driving). Because it is a pain in the ass I gave up on it and the effects weren't worth it. Getting it in some sort of bottle and keeping it off the paint and all that shit, meh, I'll pass.