WebUrbanist's essay on 3D city farms caught my eye. I think we'll be seeing a lot of this in the future. In the near future, you'll find vertical agriculture in Las Vegas. Not to feed the masses, however, but to feed the tourists. It's a start.
If we grow food vertically, we can use more farmland for fuel crops. We can also remediate depleted areas and take the strain off others by allowing them to diversify and explore more sustainable and regionally relevant farming practices and methods.
Or, vertical farms will be taken over by Monsanto, Con Agra and Kraft and we'll have plenty of genetically modified corn and iceberg lettuce for Taco Bell and McDonald's.