Volvo, the European auto manufacturer renowned with safety, uses a nitrogen tire filling on the spare tire on all of their passenger vehicles. And they have been doing it for years. Why? People never check the spare tire pressure and when the time comes to use it, its either significantly underinflated or flat. By minimizing the pressure loss in the spare tire with nitrogen tire inflation, the tire remains closer to the set pressure longer.
With the price of gas, and the impact underinflation has on fuel economy, its only a matter of time until auto manufacturers start to ship from the factory with nitrogen filled tires.