I just got a replacement PW and it's better, though I can't tell how much. I think I'm going to have to use it in the dark for awhile to see the real effect - trying it out in a dark room during the day doesn't give my eyes enough time to adjust to really see if the blotchiness is really bothersome.
Below is a pic with the old and the new side-by-side. The old kindle is on the right in the photo, the new one on the left. The "Gorbechev Problem" appears on the right side of the old unit, kinda right in the middle, or a little more on the upper part of the screen. The new unit is better, but does seem to have a spot of blot in the upper left corner. The picture has been enhanced from the original to help bring out the blotchiness.
It's also worth noting that the new unit is slightly brighter than the old at the same setting. They are about 1-2 levels apart, i.e. if the new one is at a 10, the old one would have to be about a 11-12 to be the same brightness.