Corn-based ethanol: Is this a solution?

Many people have high hopes for ethanol made from corn–that it will prevent future gasoline shortages, prevent global warming, be a wonderful investment, and improve the income of farmers, among other things. Other observers raise a whole host of concerns including scalability, impact on the environment, and impact on food prices. Why is there such a huge disparity in views? What is the real promise for corn ethanol?