Ethanol has a higher octane rating than petrol, it burns cooler and completely, as it is an 'oxygenate' (the fuel contains oxygen molecules.). It also has a lower energy content, around 30% less than petrol, and it should make an engine run more smoothly, but slower and do fewer mpg.
Good for destroying rubber components in the fuel system, especially old bikes!
Ethanol is cheaper to produce than petrol, but we never see reduce prices at the pump!