The "E10" gasoline sold in most gas stations is not actually E10. Its "up to 10% ethanol". I'm pretty sure most of it is 1%-3% ethanol, not enough to noticeably effect the mileage.
Ethanol can corrode tanks and fuel lines of cars and bikes made before ~1990 or so, but all newer cars and motorcycles use better materials which do not corrode from alcohol. I don't think it makes a big difference either way. The only real downsides to Ethanol is it will cause water to condense in the fuel tank a little bit quicker than regular gasoline (you should use fuel stabilizer either way), and it has a lower specific energy, so if you're using true E10, you'll get a little worse mileage, probably about 1 MPG.
I'd rather take my chances with a little ethanol than deal with predetonation due to using too low an octane. Just my $.02