Hacker Igor Skochinsky used DRM to load Mobipocket books onto his Kindle. Using a series of scripts, he's able to convert eBook files to Amazon's AZW format and then add the necessary serial number DRM, specialized per an individual's particular Kindle.
DRM refers to the fact that you can't view Amazon Kindle books on other devices (including your computer), or on other Kindles - i.e. no sharing, the purpose of DRM.
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).
The Kindle only allows the reading of Amazon DRM-protected content.
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.