 I previously owned a 2004 QX56 which had two significant problems and a few minor ones.  Yet it was really comfortable and absolutely great to drive on the highway.  After a year and a half, I traded it in on a 2006 model, and I've been extremely happy in every respect with the new model.  Obviously, early manufacturing problems and quality control issues have been resolved based on my experience.   My dealer experience, although limited to scheduled maintenance visits, has been superb.   The '06 QX56 is great on the road--powerful and comfortable.  The interior is very well done.  Gas mileage on the road is inverse to my speed.  At 70 mph, I get 19.2-19.5 mpg.  