My flight school has one of those diesel 172's. Pretty amazing piece of machinery. I was surprised at how technologically advanced the engine is. When I (And I'm sure a lot of other people) hear Diesel I think of a big tough truck or a HMMWV that can run on a fuel/air mixture composed mostly of sand. When I realized that that the engine had more in common with a Formula 1 race car than a Peterbilt I felt pretty ignorant. I also felt pretty dumb when I was told that they run off Jet A... not sure exactly what I thought they ran on however...

Oh, here's something you might want to consider. The TBO on the diesel is considerably lower than that of the original equipment.