Ethanol blended gas (good or bad?)

Hi guys i have a ? for you, i have been hearing alot of information about ethanol blended gas, some good some bad. I dont know how it is in the U.S but hear in Canada, some pumps are 5% some are 10 %. What do you think about this gas in these engines? (good, bad, will it cause any harm? ) I have been using shell v power gas its 91 octane and has no ethanol in it, i really dont need to run this high of octane in my mild buildt 318, but am unsure of ethanol gas in these engines. Any advise would be grateful and thanks in advance Newathis