OK, since I never weighed in last year when this thread started, the issues I had with Diesels were cost, weight, complexity, and operating temperatures. The traffic outfit I used to fly with had a 172 Theilert conversion. You had a dual fadec system, a turbo charger, a gearbox, and a constant speed three bladed composite prop, all to give a 172 135hp. It was ok for the type of flying we did, but I wouldn't want to own one myself. Hopefully Cessna's Diesel on the 182 turns out to be more reliable than the one I dealt with.