Plenty of free e-books in Mobipocket format show up fine on Kindle.
Devices like the Sony Reader, Cybook, and Kindle DO NOT have glowing LCD screens.
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).
A cheap casioppeia allows me to read ebooks around 2001.
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.