Steven B. Carrico et al. have published "What Cost and Usage Data Reveals About E-Book Acquisitions: Ramifications for Collection Development" in Library Resources & Technical Services.
Here's an excerpt:
To better determine how e-book acquisitions might affect future collection development decisions, a team of librarians from the University of Florida (UF) launched a project to assess cost and usage of e-books purchased using three different acquisitions methods: e-books acquired in large publisher packages; single-title e-books selected through firm orders; and e-books purchased through two patron-driven acquisitions (PDA) plans. . . . The authors compared the cost-usage data of e-books acquired by the acquisitions methods across the three subject areas and describe how the findings are affecting current and future acquisitions, traditional collection management, and budgeting at UF.