You can always just scrape the book's page at kindle.amazon.com. I wrote a script in js to do this and then packaged it up as a Chrome plugin that lights up when on Kindle book page, but (of course) Amazon just updated the DOM a week or two ago and now it needs to be updated to reflect the new semantic structure. This highlights the weakness of this approach. =\
Hopefully someday Amazon will provide us with an API, though I suspect that this might run against their agreements with publishers.
