Since I purchased my diesel Golf, I have driven 10,000 miles and my miliage has improved from 40/48 to 42/48. I get 600 miles to the tank of fuel on the highway. The only problem to date is a plugged water line for the rear wiper/washer. The cruise contol is ackward to use.
The power of the engine is incredible and the car will maintain accurate speed up and down hills with the cruise engaged.
I wish it had the multifunction steering wheel of the Jetta and the 4- Motion option that is available in Europe. I also wish they still offered it in the wagon version. In Europe they also offer a TDI / GTI.