One of its biggest pros would probably be the reduction of dependence on foreign oil, I guess. The process of making the stuff can be dirty itself, though. It's been a while since I've read, but a quick search found an article I found somewhat interesting.
"Burning ethanol has a mixed effect on vehicle emissions. According to the Department of Energy, E85 in place of gasoline reduces carbon monoxide by four percent and NOx by 59 percent, but it raises total hydrocarbon by 43 percent.
Ethanol is free of certain toxic chemicals — benzine and xylene — that are associated with gasoline, but exposures to those substances are so small that no one is worrying about them today. On the other hand, ethanol exhaust emissions do contain acetaldehydes not found in gasoline exhaust."
This is from an article in Car and Driver, so trusting its accuracy could be hit or miss. But it's some kind of information that could help.