Not Yet Good News
Amazon is promising textbook rentals on the Kindle that could save 80% over the cost of buying new. That is good news, and any competition to break up the cozy and price-inflated textbook market is welcome.
But Amazon is going to have to rethink the Kindle and its software before this is ever going to work. I am a huge fan of the Kindle (though I have switched my reading to the Kindle app on the iPad). But it works best reading a book straight through. Want to page back and find a particular section -- good luck. The iPad app actually works better, with a touch screen slider that allows a little better browsing. But for textbooks, they really need some kind of page navigation like coverflow in the iPod (which I hate by the way in the iPod but would love for pages in a textbook).
I've done kindle and PDF versions of TEoA (http://endofabundance.com/) and recommend that "textbook types" buy the PDF for it's page numbers (good for citing) and index.
Kindles can side-load PDFs, so the main problem is the "HTML-ness" of the kindle format.
Amazon needs to fix that up in terms of standards (footnotes, endnotes, citations, quasi page numbering, etc.)
Chegg is the way to go. Just rent the book and send it back.