Theoretically hotter fuel is better. It has more energy.
I also recently saw this video for a PICC (pre-ignition catalytic converter) system. It heats up the fuel with the catalytic converter before it enters the fuel injectors. They claim an increase of 500% in mileage on a bench-top V-8. They say they are still working on it, we'll see. Here's the video:
http://upto100mpg.com/video.htm
I also use a vaporizer device on my car and have seen a 5 MPG improvement so I know there's something to the idea.
Cheers,
Lorenzo