One of the problems with DRM on e-books is that locking e-books to a particular platform also locks the book to particular reading software. I like e-books for a lot of reasons: their portability and the convenience of being able to purchase them instantly being among those reasons. However, one of the biggest potentials of e-books, and one that is curtailed by DRM, is the potential of using technology platforms to facilitate serious reading and learning.
Software can facilitate reading and notetaking, or it can make reading and notetaking difficult. The platforms I've used to read ebooks are fine for reading novels, but terrible for browsing through a book, and terrible for note-taking. That's why e-books are not suitable as textbooks or for any kind of serious reading that requires note-taking. The note-taking features provided in a lot of the software is not only awful; it ties the notes to the software. Upgrading to a different technology or software can entail losing not only one's books but also one's notes. Export features are also dismal, in my experience.
E-books should be open, and note-taking formats should be saved in and exportable to standard formats. This would allow true competition among reading platforms, so that when one does upgrade to new technology one can be assured of being able to bring one's books, and one's notes, along to the new platform.
There is nothing so fundamental as reading and learning. Business models should not be built on systems that short-circuit technologcial potentials that could otherwise facilitate reading and learning. Locking up ebooks is wrong and backwards, and especially bad for serious reading and learning.