John, over in Domestic fuel suggests that one measure of the viability of biofuels is the number of investors that are investing into ethanol in places like Missouri, US. The state saw 15 applications in 2006 compared to 5 in 2005.
I'm not sure if he's saying such a leap in investment is a good thing. There is a danger that 15 may be nine too many, that the extra demand for corn to make ethanol will distort the market in Missouri and that there could be extra land under cultivation, or more intense cultivation, and that could have severe environmental impacts.
Still his site is worth a look...