Walk into any Lowe’s or Home Depot and look at their ceiling fans. Almost all of them are flat as a pancake. As pointed out in the Economist, quoting David Collins of Synergetics Environmental Engineering:
If blades were designed for better aerodynamic efficiency, instead of for being stamped from sheet metal as cheaply as possible, the electricity consumption of many cooling systems could, he says, be cut by a third.
Fan blades should be shaped like real airplane or boat propellers, curved with a twist, dating back to the Wright brothers. The people who design real propellers want the most thrust per unit of energy input, i.e. moving air (or water) as efficiently as possible.
Wouldn’t you want the same thing at home? (The Economist article gets in to a lot of other aspects of air conditioning systems, and improvements in the offing. Worth a read to see what’s on the way.)