Another good resource for used books is
AddALL Used and Out of Print book search. Just used it to find an international version of a textbook for a class for the spouse, 1/3 the cost of the textbook at the campus store.
It might depend on the subject, and the student's major. A chem major taking a gen ed course in anthropology might be perfectly willing to buy the anthro books in a Kindle edition, but may want a hardback o-chem text because that's a long-term reference. On the other hand, many students might want to keep their art history book.
High school and younger kids would be a GREAT target market. Many (most?) schools can't afford to have enough of those backbreaking textbooks so that students can keep one book at home and use a class set at school. Parents can't afford or can't find duplicate copies to purchase for home use. If a parent can buy a kindle and then cheaply and easily buy an e-text for home use, voila, a new market for textbook publishers and no more aching backs for students.