ethanol in gas bad for our cars?

The first year that 10% ethanol in the gas came out here that winter,everyone that put up their small engine,all had problem come spring....
I had repeat customer after customer having me look at their vehicles due to mpg loss.
Told them all it was the ethanol.
One of my customers is a landscaper and I asked him how he was dealing with it.He told me that he fills his five gallon gas cans to the top,on each gas can he has mark about 1 inch down.He leaves the lid off the gas can till it reaches that mark.He says the ethanol evaporates first and swears he no longer has problems with his small engines even after being store for awhile.
TXDart