Try making diesel fuel from it. And switchgrass doesn't grow everywhere. In fact, it doesn't grow at all much north of Oklahoma.
[blah blah blah]
Now, if you converted all those acres to biofuels, what the hell do you intend to eat? Switchgrass is kinda chewy, and doesn't taste very good.
So how many acres will it take? How many are available? I'm interested in the numbers moreso than what Rush said.
Why would you assume we would be converting current food crop land to biofuel? You said arable land, not land currently cultivated for food.