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).
As glued to the net as we all are, there's vast quantities of content that is not available online.
Kindles can read a variety of non-proprietary, non-DRM'ed formats. They read TXT, HTML, JPEG, and non-DRM Mobi files directly.
The hack allow ENCRYPTED Mobi files to be read on the Kindle. So you can buy a DRM-protected mobi book and read it 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.