Originally Posted by ShellShock
Also, if I buy a cover light for my PRS505, and in 5 years time I go out and buy a PlasticLogic reader, I would not expect to be able to use my Sony cover light with my PlasticLogic reader. But I would expect the media (ebooks/pictures) used by the device (reader/camera) to still be accessible. If fact most digital cameras will happily load pictures taken on other cameras (e.g., using jpeg format). You cannot say the same about e-Readers.
You have a reasonable chance of "longevity" if you stick with popular file formats. Eg, MobiPocket format books are readable by every eInk device on the market (with the exception of the Sony Reader), so if you stick with Mobi format (as I made the decision to a while ago) you have a wide choice of devices on which to read your books. I don't know what I'll be reading my books on in 10 years time, but I'm confident that I'll be able to get a device which will read MobiPocket books.