Paperwhite screen texture
One thing I've noticed since getting my new Paperwhite is that the screen texture is more like the actual grain of a sheet of paper than the K3's is. The K3 has a slick plastic feel to its screen while the Paperwhite has more of a 'grain' to it not unlike an actual paper page from a pbook. That adds another layer to the disappearance of the device I think. Not only do you swipe your finger across the screen rather than pressing a button like on the K3, but the texture of the screen feels very like the texture of a good quality pbook. It's something that you don't think about often on a conscious level probably, but I think it does add to the enjoyment of reading on the Paperwhite.