I recently bought a PRS-505 and have noticed that it has two stuck permanently black pixels near the center of the screen, they stay black even when the device is turned off. I suppose they don't really interfere with reading due to being so small, and i'm assuming i'll be out of luck trying to get it replaced for them, but it's rather annoying as I didn't think stuck pixels were an issue with e-ink
edit: upon further inspection they may be "reversed" pixels, when the screen turns black on page turns they seem to turn white, it wouldn't be so bad if there weren't two of them, about an inch apart pretty much dead center in the screen