[the.Mtn.Man]

One suggestion I've come across is that the screen protector/light diffusion layer isn't actually being damaged but that it is lifting off from the e-ink screen. This would explain why there is no perceptible damage until you turn the light on and see the hot spots, and it also explains why devices seem to spontaneously develop hotspots even when people have cared for them meticulously, or in cases where units fresh out of the box exhibit this problem.

Whatever is causing it, it's a pretty serious design flaw, and judging by reports at the official Nook forums, Glowtouch owners are having to regularly exchange their devices as they inevitably develop hotspots after a few weeks of use. One poster made the cynical suggestion that Barnes & Noble is eventually going to declare that hotspots are "normal" and refuse to accept returns for that reason.