Have you ever wondered how long a bistable display could retain its image? Keith Bellamy of Kent Displays
was present at the SID 2006 conference
in San Francisco where he demonstrated a monochrome display panel based on Kent's Cholesteric LCD (ChLCD) technology that has not been refreshed for 12 years. Most fascinating, the display shows no sign of image burn-in, ghosting, or other artifacts that would have been common with other display technologies after such a long time [Edit: As correctly pointed out by astfgl, from this example alone we cannot tell if that is indeed true, however, it's a claim made by the manufacturer which I like to believe it.
[via Dvorak Uncensored