I am the happy owner of a 2002 F350 single rear wheel Crew Cab longbed 4WD 7.3 diesel. I purchased it used after the original owner put 96,500 all highway, non towing, no camper miles on it in just 22 months (he worked as an oil field service rep in West Texas). It now has 244,000 miles and has served as an in-town daily driver for 5 of the 10.5 years I've owned it. Today and for the forseeable future, it serves as a rolling toolbox for trips to family vacation homes at the beach and in the mountains, a weekender off-road explorer in the southern and central Blue Ridge, Smokies, and Alleghanies, and an occasional cross-country transport to WTW trips to MT and ID.
I have enjoyed virtually trouble-free motoring with the Ford. Yes, I've replaced lots of "wear parts", including sway bar bushings, u-joints, carrier bearings, front wheel bearing assemblies, HPOP O-rings, and front leaf springs and bushings. I'm on my 3rd water pump and 3rd serpentine belt. Lightly loaded and gently driven, I still see fuel mileage in the high teens (17.5 to 19.5 mpg) and even towing my 2,500-3,000 lb popup camper I've seen only slightly lower mpg.
The weak point is the automatic transmission. I wanted a 6-speed manual when I was shopping for a used one in 2004, but they're scarcer than hen's teeth here in the East. The 4R100 automatic is prone to early failure, often torque converter failure, which trashes the whole transmission. The original owner had been hyper-vigilant about trans fluid and filter changes and I have changed it 5 times since purchasing the truck. Last week, I purchased 20 qts of Mobil 1 synthetic ATF, an internal filter, and a new in-line filter for a 6th ATF change scheduled for this Saturday. Perhaps using synthetic ATF and a Magnefine in-line filter, plus keeping a sharp eye on trans fluid temp, has allowed me to enjoy longer then normal 4R100 life.
As to a diesel sitting for long periods, it need not do so. I make sure I drive mine at least around town a bit once each week. There are fuel stabilizers, including biocides, which you can add to the fuel to keep it fresh. Anti-gel additives should be used in winter. Use of additives can be combined with careful selection of fuel retailers (purchasing only from high-volume sellers such as busy truck stops) to minimize fuel problems. The only fuel problem I've had in + 10 years was driver error--I ran it out of fuel. A diesel can be the devil to re-start after running out of fuel.
So that's one guy's story of diesel pickup ownership. My Ford is, hands down, the best truck I've ever had, and I've run nothing but 4WD pickups, Scouts, Jeeps, and Suburbans since 1973. As to more recently manufactured diesels, they do seem to have a plethora of issues, most related to the increased level of electronic controls. Practically every guy hearing of my long-lived 2002 says "Man, I wish I'd never traded my 7.3". Perhaps its status as a large displacement, de-tuned laborer provides a level of long-life and reliability, or perhaps I've just been lucky.