I don't know if this has been mentioned here already if so, please forgive me
but I didn't want to read 196 pages just in case:
I'm on a Kindle Touch (K5) and almost all of my custom screen saver images have an imprint of the last visible screen on them its not very strong but definitely visible. Like if I was on the home screen, you can see the KUAL button and the example book thing shine through the image if I was inside KUAL you see the menu buttons shine through.
Its not a big issue but still kinda annoying if you know its there :S