Oh well - should make our Mobi downloads more popular, at least

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I would GUESS (and a guess is all it is) that the Kindle is a standard DRM-encoded Mobi file, and that the sales mechanism will encode it for the user's registered device automatically. IF that's the case, and IF the Mobi PID is accessible somehow, that would let Kindle owners buy other Mobi books. What it will NOT do, of course, is allow non-Kindle-owners to buy Kindle books.