There was a good article about this in the Enthusiast a couple of months ago with a lot of explaining from one of Harleys powertrain engineers.

Ethanol will degrade rubber, however the "rubber" seals in your engine and carbs are not plain rubber. They are more sophisticated compounds which are not broken down by Ethanol so you are safe to burn E10. Not only is it safe, it's the recomended fuel fora new HarleyDavidson. I really have a hard time believing that some of you run the Super Premium gas from your filling stations and that it doesn't have Ethanol in it (unless you've found someplace that sells leaded gas to the general public).

 

Stanford University just completed a study that shows that ethanol pollutes the air as much as gasoline and biodiesel pollutes more than regular diesel. It does take just as much energy to produce a gallon of ethanol as the gallon of ethanol has in it. Burning a 10% blend of ethanol to gas results in 10% decrease in fuel mileage. Ethanol has much less energy (BTU) than gasoline. Repulsivelicans favor ethanol as much as anyone else, for the same political reasons as anyone else. My own vehicles run like $#!+ when I use gasohol.
Disclaimer: Most of my income is from growing corn and soybeans. But facts are facts.

 

Mileage decrease is not 10% on E10, b/c Ethanol is not so below the energy output of gas that the % used as fuel is the reduction in mpg. And studies have shown the entire end-to-end production of ethanol produce MORE energy than it takes (even more so when the 'trash' ethanol methods are used instead of grain. My vehicles run fine w/gasohol, and I am getting 32mpg in my car and up to 40 on my bike using it.

And what some studies try to say is that ozone increases when using ethanol. The pollutants from gas are vastly reduced w/ethanol.