Here's an interesting find: A greenhouse designed to take in seawater and desalinate it while cooling and irrigating the crops. The cool and humid air reduces the need for irrigation (by a factor of 8, apparently.)
The design is pretty neat - low energy, not terribly complex, and would open up new areas of land for agriculture. It's the usual problem with these kinds of projects, though: High capital costs and low operating costs.
I can think of at least one problem with scaling this up, though: A network of seawater pipelines feeding a large number of these farms poses a potential disaster in the making. A burst saltwater pipeline could ruin a large patch of land.