One thing that struck me in the debate the other night was McCain's forceful opposition to ethanol subsidies. He is, of course, right about this -- corn-based ethnanol is economically and environmentally suspect -- and I respect him for saying this. It nonetheless seems to me that this could be used against him.
McCain's comment effectively seals the deal in Iowa, which leads the country in ethanol production.
If you look at the list of ethanol producers (here), the next largest ethanol states are Nebraska, Illinois, Minnesota, and Indiana. Of these, only Illinois is not important. In Nebraska there is the electoral college of CD-2, and Minnesota and Indiana are both potentially in play.
Given that the relevant counties should be easy to identify, and given that most of the beneficiaries of these subsidies are likely Republican-voters, a micro-targeted message could be effective in changing some Republican votes or (more likely) suppressing them.
But given that some of these states could be very close, shifting a few thousand votes and suppressing a few thousand more could make a difference.