Time for me to chime in. I decided to try acetone in two of my vehicles to see what would happen. I tried it in my 05 F-150 with the 5.4 3 valve, fuel injected Triton motor and in my '87 Zuk Samurai, which is (poorly) carbureted with an aging 1.3L 4 banger.
After approximately 1 month of use in the F-150, I notice absolutely no improvement in gas mileage, performance or motor vibration. Zip. I have discontinued use with the F-150. It may be improving my emissions, but since we do not go through emissions testing out here, I have no way of verifying how much better the emissions are.
After roughly the same usage in my Samurai, it runs smoother, starts easier, and gets about 10-15% better mileage than it did on plain gas. I started using it about 2 tanks after I did a motor swap, and the improvements are all on the new motor. I will continue to use it in the Samurai.
As these are two significantly different fuel systems, I'm wondering how much the fuel management system, head design, intake design, etc. are affecting these results. From my VERY limited tests, it appears that the more sophisticated motors benefit less than the older motors, which makes logical sense. The newer fuel systems and motor heads are better designed for more thorough combustion and cleaner emissions.
Has anyone else run acetone in multiple vehicles? I'd like to see some data that would either support or refute my theory.