That is, if you've bought a book through Amazon, they'll now sell you the Kindle version for $1-$3.
http://gizmodo.com/amazons-giving-you-discounted-digital-copies-of-physic-1244273998
I've bought a few books that include a CD with the Logos file and unlock, but this is an interesting move on Amazon's part. I don't see Logos being able to match that, since they have no proof that a Logos owner possess the physical book. Logos certainly has major advantages over Kindle format, but if you want the book AND file, this is tempting.