JISC has released JISC National E-Books Observatory Project: Key Findings and Recommendations. Final Report, November 2009.
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 summarises the key findings of the project and the recommendations for future action. . . .
The final report summarises the findings and data captured through deep log analysis, focus groups, user surveys and print sales analysis. I recommend that if you wish to see more detail that you read the relevant reports and look at the original data that is also available. Please see the reports page for further information and for the individual reports.