Being at home on a rainy day, but wanting to read some new novel that just came out, you can have it in seconds. This concept (not hobbled by DRM) is pretty damned liberating.
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).
Amazon can do a lot of money only from selling kindle, like Apple does with the iPod.
Non-DRM Mobi books, like free e-books found online in Mobi format, or files you convert to Mobi files, are already supported on Kindle.
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.