Saw this article about the cost of ownership issues with the new Kindle:

The Kindle DX runs you $489 as an upfront investment, and the average student spends $488 on new and used course materials a year. In a nutshell, Amazon is asking the average student to fork over more money for the Kindle and then buy the textbooks too.

Add it up and the average student is losing money on the Kindle DX in that first year. Let's say Amazon can halve your textbook costs to $250 a year–you'll still be shelling out nearly $750 in year one.

Over two years, a student will still be behind on the Kindle DX return. Going the paper route on textbooks yields a two-year cost of $976. But the Kindle still runs you $13 more over two years.

Source: With Kindle, why is Amazon blind to Wi-Fi? | Wireless – CNET News

One of the problems the article points out is the used book market and how students buy used books then sell them back since most students don’t want to keep their textbooks forever. 

So here’s the solution: Work with the publishers to rent textbooks on a per-semester basis.  At the end of the semester, the books expire and can’t be used.  Done properly, this could eliminate the used textbook market, a market that publishers and authors hate because they don’t make anything from it.

I’d much rather pay $25 or $50 to rent the book for a semester than play the book buyback game.  Especially since I usually lose it.  For example, I bought one book for a small class that set me back $130, and they only had it new.  I sold it back for $20.  Net cost to me was $110.  If I could have paid $75 to rent the book for the semester, I’d have done it.  And sometimes the used prices are so screwy that I just buy new to begin with: When the book is $80 used (and scribbled in) or $100 new, I usually just pay full price.  When I sell the book back, I usually only get back 30 to 40% of the price. 

There already are some book rental services, but they require me to deal with shipping and have limited selection.  E-textbook rentals could eliminate both problems.  Plus, the money I’d spend on renting the textbooks would compensate authors, and not bookstores who rape me on used books.