I have owned gas pick ups and currently own a 92 F350 diesel. From my experiences, the diesel pick up is advantageous if one or all of the following criteria are met:
1. You do a lot of long distance travelling.
2. You consistently carry heavy loads.
3. You're pulling a heavy trailer.
4. You intend to keep the truck a long period of time.
I love the diesel engine on my truck. It's sound, power, torque and decent fuel economy are terrific. However, what I have found is the fuel economy isn't as great as you would be led to believe (my truck gets around 16 mpg on the old 7.3 diesel), routine maintenance is more expensive (e.g. oil changes are close to double) and repairs can get costly (I had the injectors replaced last year. It cost me $ 2 000 Canadian. The Ford dealer told me that the Powerstroke would have been double that).
On top of this, like others have mentionned, sure the diesel will have double the life expectancy of the gas engine. However, the rest of the truck won't. In addition, the upfront cost of a diesel is more than what it would cost to replace a gas engine.
Nonetheless, I still think I would go with another diesel for my next truck. However, since I only use the truck, for stop and go lawn maintenance and landscaping, I would definitely think about the gas engine.