Yes Pimentel has been discredited: by the Ethanol Lobby, but not yet by science.
The US gasoline consumption is 9.5 million barrels / day, 9.5 * 365 * 42 = about 145 billion gallons annually. The US annual corn crop harvest is 10 billion bushels. 10 * 2.5 = 25 billion gallons of ethanol. Ethanol yield is about 2.5 gallons per bushel. 25 / 145 = about 17% If we used the entire annual corn crop to produce ethanol, 10% could be used for gasohol while the other 7% would be consumed by increased demand before the new ethanol plants came on line.
In addition to corn I have been looking at some numbers on soybeans and potatoes.
The US harvests about 2.5 billion bushels of soybeans annually, and about 23 million tons of potatoes. Potatoes yield about 25-30 gallons of ethanol/ton or 688 million gallons of ethanol about .5% of our gas consumption.
There has been much talk about bio-diesel from soybeans. The only numbers I can find are that soybeans yield about 9.5 to 10 pounds of oil/bushel. How much bio-diesel will 10 pounds of soybean oil yield?? 1.5 Gallons max, that would make 3.75 billion gallons of bio-diesel. Our annual distillate consumption is 4.5*365*42=69 billion gallons. Soybean bio-diesel would only supply 5.4% of our distillate needs. 3.75/69=.0543.
There is another problem with bio-diesel. Currently an average to excellent soybean yield is about 50 bushels/acre. At $6.00 a bushel that is a $300 annual/acre crop, However at best it will yield about 75 gallons of oil and 60 gallons of bio-diesel. That means with zero capitol and processing expense, the bio-diesel has a crop cost alone of $5.00 per gallon.
I understand that Minnesota has enacted a 2% bio-diesel law that requires nearly all diesel fuel to be blended with 2% bio-diesel. Now I don't know how much nearly is, but here is a web-site to explain it further.
http://www.mda.state.mn.us/biodiesel/b2/default.htm
Here is a web-site of oil yield for oil-bearing crops.
http://journeytoforever.org/biodiesel_yield.html#ascend

Here is a more efficient method of consuming corn. 15% water in shell corn contains 7000 btu's of energy per pound, and 15% shell corn weighs 56 Lbs per bushel. That is 392,000 Btu's per Bushel. At $2.00 per bushel that is $5.10 per million Btu's. Then I checked kerosene it's about the same as distillate. 6.819 Lbs per gallon and 19,810 Btu's per pound or 135,000 Btu's per gallon, or 7.4 gallons per Million Btu's. At $1.76 per gallon that is $13.00 per million Btu's. NG spot today was about $10.00 per million Btu's. Now according to the USDA a bushel of 15% corn should yield 2.68 gallons of ethanol,and ethanol contains 14,000 Btu's per pound and weighs 6.59 Lbs per gallon. That means that a bushel of corn will yield 247,000 Btu's, so you see you lose 145,000 Btu's in the ethanol process, however the leftover mash is used for cattle feed. I don't know the efficiency of a corn burning stove versus a gas or fuel oil furnace, however it is certainly more efficient than using it to produce ethanol, as a significant amount of energy is used in the conversion process. Corn burner web sites.
http://www.bae.umn.edu/extens/ennotes/enaug01/burncorn.htm
http://energy.cas.psu.edu/shellcorn.html
http://www.breitbart.com/news/2005/12/09/051209141924.flu6l9pn.html

How much food value does ddg have after 65% of the energy has been removed?