Since New York Times' article on vertical farm which I have blogged before, there is a bit of interest on the blog sphere on that.
Saving valuable land space for food production in City is a great idea, but there is one important consideration which seems to be missing in all the reporting.
Plant grows by photosynthesis. Photosynthesis needs light. In a high rise structure, which would be quite wide and deep, there will be the issue of getting light into the centre of the building.
At the end of the day, all the energy we have come from the Sun. If we are going to use renewable energy, that will be dependent on the amount of sun light (and wind which is caused by the Sun shining on nearby land mass) available to the building. I am afraid in reality, vertical farm, without additional energy input, would only be a good idea on paper.