I got one of the first 08 2500HDs off the line as a custom order back in Aug. 07. For what I paid, this truck is an amazing value when compared to the F250s and Ram 2500s out there. The gas V8 has plenty of power and tows a 5000 lb trailer with ease. At first I had a problem with the transmission not downshifting easily in the 25-50 mph range, but the dealer flashed the ECU and now it's more responsive (although a bit less smooth- shifting - before it was like silk). Fuel economy has been mostly around 10-11 in the city, anywhere from 12-18 on the highway (the faster you go, the worse it gets). Most impressive is the quality. The interior and overall feel of the 2500HD is very solid.
Gas V8 power. Smooth 6-speed auto. Front seat comfort. Interior look & quality. Exterior build quality. Not that rough of a ride (much better than my 01 Dodge Dakota and 04 Tacoma). Superb value for what you get.
Make sure you get the ECU flash for the tranny, which makes it more responsive downshifting in the 25-50 mph range. Otherwise, 11 months and 12,500 miles later, no issues.