Diesel is NOT the answer to every economy and emissions problem. Remember folks: diesel fuel is a BYPRODUCT of refining gasoline. If everyone started driving diesel vehicles diesel prices would go through the roof! A 42 gallon barrel of oil produces 20 gallons of gasoline and only 9 barrels of diesel. You really can't just change this ratio at will. The absurd diesel prices from the summer of '08 should tell you what happens when people stop buying gasoline: truckers and cargo ships still have to buy diesel so the prices skyrocket!
Technologies like cylinder deactivation and gasoline direct injection are MUCH better investments than diesel cars.