I've owned a total of 3 DS's......2 old-style and 1 DSlite.
My first DS had 2 dead pixels in the top screen and I exchanged it. The second one was (and still is) still working perfectly. I have since sold it to my niece after I bought the lite and she loves it.
Now I have a black DSlite. As far as I can see, it's essentially perfect. No dead pixels, all the buttons still work, d-pad is fine, no hinge cracks, the screens are centered in the casing well and no issues with the touchscreen. I bought it about a week after black became available in the USA.
I do see a gold color between the left area where the two parts of the hinge meets, but I think that is normal and you see it more just because it's a black DS.
As for scratches....those are gonna happen no matter how careful you are with it, but I have screen protectors and the "Retro" skin from decalgirl on it, so those take the beating instead.
I consider my DS as perfect as I could hope for.
EDIT: I guess it would be worth mentioning tthat I don't take my DS everywhere with me. It's a home diversion. This is not to say that I NEVER take it places, just that I don't most of the time. That could be why mine hasn't developed any problems.