Only got a chance this AM to skim this article from Library Collections, Acquisitions, and Technical Services, Volume 29, Issue 1, March 2005, Pages 71-81. Electronic or print books: Which are used? (non-proxied link to Science Direct).
The authors describe a study done at Louisiana State University where they compared the usage of books that were held both in print and through netLibrary and found that overall, print was used more than the electronic version of a title, but they offer some caveats and suggestions about how to interpret that result. Distance Education was mentioned only in passing. I remember seeing some statistics about eBook usage here at the U of C and they showed some similar trends. A lot of the eBooks never were used, but some of them were used dozens, if not hundreds of times! Tough to get that much usage out of a single print copy, eh? As the authors of the article point out, there's no way of knowing if the whole eBook was read, or if it was just a chapter or less that was really used, but they also remind us that we don't know that information about traditional paper book usage either.