Originally Posted by ProDigit
A strong changing magnetic field can destroy feeble electronic equipement indeed; however if a magnet is gently applied and removed I see no harm.
Acording to the theory, the e-ink screen should become black(or white) when applying a magnet on it depending on the polarity of the magnet.
So far doing so does not change the screen not even under prolonged periods of time.
At least not on the Sony Reader PRS-505
My Sony PRS505 has small magnets in the body(*), so I think I'd be alarmed if a weak magnetic field caused eInk screens harm!
(* Definitely the body and not the case - small metal objects will stick to the relevant areas of the body, but not to the case)