From my understanding ethanol makes less power per unit than regular gasoline. So that means all these stations using the 10% ethanol blend, are selling you less potent fuel. 10% ethanol would mean that fuel potentially makes 10% less hp than an equal amount of regualr gasoline.

How does this effect you? Well that depends...in a car like mine, that is by no means optimized, it doesnt effect much. In a more sensitive car, say a 350z, or a well tuned car, this could be a big difference.

IE: Sport Compact car magazine tested a 350z (bone stock) with 93 octane fuel, then again with 100 octane...they gained something like 7hp with the 100. They said with the 93 it was visiting the knock sensor a lot. Thats what inspired the 100 octane test. So you figure, with the 10% ethanol 93, that same car could potentially show hp below stock levels.

Unfortunately I think the 10% blend is FL law now. Bad news for anyone trying to really max out their car.