Hack let you convert encrypted Mobipocket files that were intended for another reader so that that work on Kindle.
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).
Granted the PDF converter seems to have some trouble with graphics PDF's, but for books the converter works very well.
As glued to the net as we all are, there's vast quantities of content that is not available online.
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.