I got my KPW yesterday (first Kindle I own, no previous experience with Kindles), and I was happy to see that my unit seems to be OK, the lighting is fairly even, but the shadows between the LEDs are quite pronounced (though not a problem for me). No discolorations as far as I can see.
However, I am unsure if the screen is as crisp as it should be. It isn't blurry, but it isn't really crisp either, if you know what I mean.
There is also another annoyance: There seems to be an occasional random skipping of multiple pages. I touch to turn pages, and suddenly it jumps to some random location. I'm not alone with this, it seems, and I've replied to this thread also:
As I wrote in that reply, my KPW is from the 503 batch, and it came with version 5.3.1 installed. Perhaps better to start a separate thread on this issue on these boards too?