For me it was not to use unleaded with ethanol in the lawnmower. It seems that ethanol being a grain based fuel absorbs moisture which reduces the efficiency of the motor during wet weather conditions. The mechanic at the mower shop put me on to it when I couldn't get the mower to run properly. My mower had a complete overhaul in December so I knew it was a fuel issue.

Knowing this I will not be using the stuff in the car.