If anyone's curious about all the different issues being mentioned, I can confirm/explain a list of the ones which apply to my pre-Pearl e-ink device w/ the OpenInkpot drivers. [Otherwise you can skip this; I don't have a Nook
].
1) Even with full screen refresh, room temperature, and no direct sunlight, I can always see
some "ghosting" of the previous page if I look very closely.
2) If you enable "partial screen refresh", the ghosts "pile up" on each page turn, until the next full screen refresh. Personally I prefer to leave it on full page refresh; as others have mentioned it doesn't seem to slow it down too much.
3) If I let the device get cold e.g. when reading outside, the screen refresh pattern is different. It appears to flash even more - I don't remember the exact pattern. I discovered this is actually controlled by software. If you shell into the device, you can see a temperature sensor. There's a daemon that polls the sensor and switches between a couple of different control patterns. I assume the display elements need a bigger kick when they're cold :-).
4) On
my display, direct sunlight can cause the image to actually fade and/or show even more ghosting, over a period of several seconds, to the point of near unreadability. This is the manufacturing defect, which caused Sony and other reputable producers to accept returns. It's said that they basically forgot to turn on the manufacturing stage which added a UV-protective layer. I don't think it's about the display getting too warm, because it fixes itself very quickly if I move into the shade. It's just vulnerable to a certain type of em-radiation. Note that E-Ink adjusted their testing, so in theory more recent batches like the Pearl displays should be free of this specific defect.