And the Kindle reader for the Mac is out in the wild:
(Click for larger)
Read Kindle Books on Your Mac
Get the best reading experience available on your Mac. No Kindle required
Access your Kindle books even if you don’t have your Kindle with you
Automatically synchronizes your last page read and annotations between devices with Whispersync
Create bookmarks and view the annotations you created on your Kindle[From Kindle for Mac]