I think it's still worth it even with high diesel prices.I have a diesel Renault Clio and I'm getting an average of 4.6 l to every 100 km or 21,7 km per liter.Try that with a petrol engined car.Admitedly it requires a smooth driving technique ie going slower,but as I'd rather spend my money on the boat than at the pump it's well worth it.Another alternative is LPG.It's usually very much cheaper,and cleaner,than petrol.