Yes, it works. My Jeep CJ went from 12 to 16 Mi/Gal and my Honda Accord went from 28 to 31 Mi/Gal. These results come from many repeats using a very regular and boring commuter route.
It breaks down dispersion forces in hydrocarbons allowing for more of the air/fuel mix to be atomized.
Acetone is a common ingredient in many gas formulations.
My neighbor is an engineer for a supercharger mfg for Mercedes. I have a Ph.D. is organic chemistry. We both agree that gas formularies can have a significant effect on mileage.
Edit: Gasoline is a very complex mixture of organic molecules that whose composition varies alot from region to region. Some of this is due to variations in the composition of the distillate, and due to the different additives that are added to gas and vary from region to region. Other variables than can affect the effect of acetone in gas are the type of engine, type of carburetor or fuel injection, the level of tune in the engine and the driving style.
I am not the only nerd who has been fiddling with various gas additives including aromatic amines (smelly), branched chain ethers and epoxides, long chain fatty acids, detergents, micelles, .... the list goes on and on.
In the final analysis, a well tuned engine introduces a completely atomized air/ fuel mix into the combustion chamber which is, in turn, completely burned. Fuel condensing into droplets is often not burned and goes out the tail pipe as waste.
Acetone can help in this as it also helps water in the gas to be burnt up as well.