The JISC just released a study on E-book use in the UK. Their "National E-Books Observatory Project: Key Findings and Recommendations" are presented online in..of course, an e-book at http://www.jiscebooksproject.org/archives/335
Here's an excerpt from the press release:
"The results of the two year project exploring the behaviours of e-book users and the impact of course text e-books on print sales are now available. The final report summaries the key findings of the project and the recommendations for future action... captured through deep log analysis, focus groups, user surveys and print sales analysis."