Couple facts you should clarify before making statements like:

"Climate pollution is released into the air when American farmers switch their land from growing food to growing fuel, and South American agricultural interests burn the rainforest to clear land to grow additional food to fill the gap."

That's a hypothetical statement not supported by facts. I think you must know this. Amazon deforestation (down considerably in recent years) is driven by 1) lumber harvest and land grabbing (only 4% is titled... take it and its yours, apparently, and Amazon rainforests are rarely burned because of lumber value), 2) more land for cattle, the second use that's been observed regularly, also now declining, and 3) any crop eventually, but no biofuel crops have been observed. I think this is a myth invented by big oil.

I'm going to add another comment on this with another fact you should consider, quoting you again:

"(like anyone who pays more for food as a result of ethanol mandates)" is repeating a fallacy. Oil prices, weather and commodity speculation had a lot more to do with food and corn price increases last year. Both the price of corn and the food CPI are down this year, and ethanol production has increased. 

This past year, the cropland devoted to corn in Brazil decreased. Where is there an indirect land use effect here? There is not one, as hypothesized.

I agree with your cautions on offsets. USDA might be stupid enough to credit no-till conversions even as farmers upped their glyphosate applications. The entire agribiz establishment, in which I include USDA, appear to have no idea that more chemicals and GM crops that depend on them are absolutely not sustainable. There is no carbon benefit to be had there. Somebody should do a life cycle/land use study on it.

The GM and chemical companies have studiously and successfully avoided soil and ecosystem impact studies, by the way, so this isn't as far-fetch as it may sound.

Good post. Thanks.