The irrational exuberance over ethanol that swept through the American corn belt over the last few years has given way to a dreary hangover, especially among those who invested heavily in the sprawling production facilities now dotting the rural landscape. It's the Midwest's version of the tech bubble, and in some ways, it is remarkably familiar: overeager investors enamored of a technology's seemingly unlimited potential ignore what, at least in retrospect, are obvious economic realities.

More than a hundred biofuel factories, clustered largely in the corn-growing states of Iowa, Minnesota, Illinois, Indiana, South Dakota, and Nebraska, will produce 6.4 billion gallons of ethanol this year, and another 74 facilities are under construction. Just 18 months ago, they were cash cows, churning out high-priced ethanol from low-priced corn, raising hopes of "energy independence" among politicians, and capturing the attention--and money--of venture capitalists from both the East and West Coasts.