I don't know if everyone is aware or not, but in the UK nearly all our petrol we buy in the UK has at least 5% ethanol in it. It was going to go upto 10% for 2013 but has been delayed.
I was talking with a bike racer/tuner today that was telling me that people are starting to see problems with it.
It's said that it goes 'off' a lot quicker, as little as 90 days. It 'wicks' water, bit like brake fluid does. It can 'change' the results of a plug chop ( I didn't understand this ), so proper engine management is more important. It can rot rubber, fibreglass, etc and can have an effect on laying our bikes up for the winter.
Helps the environment though