I know of very few major mechanical issues. Its the little things like poor interior plastics, fit and finish, oil consumption on some models, ect.
I remember comparing the 04 F-250 we still have to the 05 Dmax I also had. The sheet metal was very thin compared to the F-250, doors felt 1/2 as stout, there were squeaks and rattles plus loose interior panels on a 9 month old truck, ect. The body lines were not even. It was the little things that added up to me.
As I have said before this is changing. I spent 2 days with a new Chevy Malibu last week on a flight to Ruston, LA. There is noting to do there. This rental car had under 1,000 miles on it. I went over it with a fine tooth comb and drove it about 150 miles killing time. I can honestly say it was by far the finest GM product I had been in period. Its fit and finish was the best I had seen. The had fixed the issues I had seen with my 05 Dmax and the Saturn I just sold about 8 months ago.
I also rented a new 2011 Buick Enclave last week in St Louis. It was very nice also. I only drove it about 20 miles and had it for just over 6 hours.
As for selling cars and trucks there are a couple ways to do it. You can have quality, price, warranty, ect. GM and some of the others have touted big warranties to draw customers away. As builder stated GM lacked in the diesel game. The big warranty on the Dmax sold lots of trucks. I am not being biased here. I am strongly considering a new F-150 with the 3.5 twin turbo V6. The twin turbo V6 scares me a little but the big warranty Ford is offering on them is helping to sell me on it. Hyundai also went from a tiny little company to now a leader in the small car segment. They had something like 48% growth last year. Warranty and price sold lots of cars for them. If I were looking in that segment I would now put them in front of Honda and Toyota.
As for GM as a whole I still stand behind my words and say that around 07 and later is when you started seeing major improvements in not only materials but the fit and finish. By 2010 they were on par with the rest.
Chris