From Walter Younquist's Geodestinies* (1997),

p246:

"Considering all biomass sources, the total volumes of raw materials needed to produces enough liquid fuel to make a substantial substitute for oil really do not exist. The United States currently consumes more than 18 million barrels of oil a day. A barrel weighs about 310 pounds, which means that each day some 5.6 billion pounds (2,395,000 metric tons) of raw material would have to be grown and harvested each day, winter and summer, 365 days a year. With the energy costs of planting, plowing, fertilizing, harvesting, and processing, the net gain in energy would be very small, so the actual amount of net energy produced would probably be equal to less than 20% of the total oil produced. Replacing any very appreciable amount of conventional oil now used with liquid fuel from biomass seems quite unrealistic. Biomass cannot supply even a modest proportion of the current oil consumption in the United states nor anywhere else."

Cited on page 244:

"About 72% more energy is used to produce a gallon of ethanol than the energy in a gallon of ethanol."

Food, or fuel. Difficult choice. May help the transition, but not a substitute.

* which I see is out of print. Rats. This is a really good book.