I would really like to here Amazon's arguments for not using ISBN (or Goodreads IDs) for matching books on Goodreads...
Ok, for PDOC to = no X-ray, no sharing , no this, no that, BUT... you should at least be able to add a book with metadata containing correct ISBN to a Goodreads shelf and update % read. Not that I've ever kept my Kindles online in this 6 years of owning them

I would still use Goodreads for Android app rather then built in solution on Kindle...
But yeah, real subtle encouraging :P