Simon Donner today answered a bunch of questions I had about US food production numbers:

[T]he extra corn for ethanol has to be planted on productive croplands, lands with the right soils, and most of that land is being used. In 2007, soybean planting – the other major feed crop grown in the midwest US – went down 16% in the US to make space for more corn. Soybean exports and use remained the same, but the ending stocks were down 72%. In other words, we’ve been cleaning out the cupboards.