We ferment corn for the same reason u eat it. It is quick and cheap to grow, we have a ton of it, and the sugars in it are easily broken down. Wood, grass, and all the other stuff you hear about being the next big thing dont have these artibutes. Cane Sugar is even more energy dense and easily fermented, but we dont have the climate here in the USA for enough of it. They maybe could grow enough in Hawaii to take care of their needs, but other than that we will need to import it.
Everything other than corn, sugar, or the equilivants (wheat, sugar beets, etc) is years and years away from being ready to cut your gas bill.
