A recent issue of Nature published an article by Declan Butler called "Technology: The textbook of the future" included a paragraph about OhioLINK's exploration of digital textbooks:
Ongoing tests of CourseSmart e-textbooks by the University System of Ohio show that they reduce costs -- the average US student forks out some $900 annually on print textbooks -- and students using them perform just as well as when using paper versions, says Peter Murray, deputy head of new service development at the Ohio Library and Information Network in Columbus, Ohio, which assists the University System of Ohio on the project.
I'm afraid I didn't clarify the particulars of our efforts in the phone call with the reporter. Our test for effectiveness of electronic course materials was with a category of materials we call "enhanced textbooks". They are the platforms that offer not only the text but also links to videos, glossary terms, pre- and post-texts, supplementary reading materials, and simulations. Examples of these are Wiley Plus from Wiley Publishing and the Campbell/Reece biology offerings from Pearson. Another program of the University System of Ohio is the featuring page-for-page replication e-books from CourseSmart. We have not tested the CourseSmart material for effectiveness compared to the identical material in printed form.
Butler, D. (2009). Technology: The textbook of the future Nature, 458 (7238), 568-570 DOI: 10.1038/458568a
The text was modified to update a link from http://universitysystem.ohio.gov to http://web.archive.org/web/20090326141957/http://uso.edu/ on November 13th, 2012.