When you fetch a cover image for a book from LibraryThing, it's rather small (140xsomething), causing it to appear very pixelated on the Reader's screen. Now, the images on LibraryThing link to Amazon, and it's easy to change the link to include a larger cover image.
Example:
http://www.librarything.com/work/153691
Links to this cover image:
Removing the SX140 part from the link causes the original large cover image to be downloaded:
In fact, knowing how Amazon builds the cover image urls (
http://images.amazon.com/images/P/ + IBAN + .01._SCLZZZZZZZ_.jpg), and given the fact that LibraryThing simply links to the Amazon, it could be just as possible to directly download cover images from Amazon without the need to go via LibraryThing first.