A cheap casioppeia allows me to read ebooks around 2001.
Typically ebook readers are larger than PMP's with larger screens. If you're going to read for a few hours, then the screen of a typical PMP becomes pretty eye-straining (due to size, contrast, and brightness).
There are converters available from Amazon and/or Mobi for pdf and doc files.
Amazon can do a lot of money only from selling kindle, like Apple does with the iPod.
A revolutionary portable reader that wirelessly downloads books, newspapers, magazines and blogs to a crisp, high-resolution electronic paper display that looks and reads like real paper, even in bright sunlight.