If you read some of the Kindle discussion groups, you'll see people complaining about "no backlighting", and then a few days/weeks later they will be lauding the fact that it has no backlighting.
Ebook readers have extremely high contrast/readability and are extremely energy-efficient, being able to display several thousand pages of material without needing to recharge. eBooks are a narrow product, but they have their own ways in which PMPs cannot compete.
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.
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).
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