i bet its a little bit of all three problems getting clumped toghether,
thier is always a chance any card from anywhere could be faulty, so that explains it i mean, sometimes things get bounced around to much off the assembly test line during shipping, not all silicon is created equal and some parcel packers have bad days and im sure take it out on the parcels.
just like some cards handle much higher clocks at lower voltages than others some card due to design work better at extremely low clocks when starved for power,
not all components play well toghether, thats just the nature of the beast,
my 4870, and 5670 have worked flawlessy on windows 7 ultimate 64 bit edition thus far.