First, not a huge fan of ethanol, especially from corn. There are much better things with which to make it, if you're dead set on making it.
Second, I think CRP land is generally a good thing. I've dealt a little with implementing it, and worked quite a bit on managing it. I know that it can be a little iffy on who gets to sign up for it and who doesn't, but that's mostly internal FSA crap. Most of the land I've worked on wouldn't be that great of farm land anyway (in Western KY). With that said, properly managed CRP provides much needed habitat for wildlife. It's generally good for quail, rabbits, and other upland species (think random birds that don't get any respect). CRP is a very broad term that covers many practices with various goals. It includes stream buffers, field borders, conversion to native warm-season grasses, hardwood restoration, I think there are some grazing version, and other things.