Tina E. Chrzastowski and Lynn N. Wiley have published "E-book Use and Value in the Humanities: Scholars' Practices and Expectations" in Library Resources & Technical Services.
Here's an excerpt:
The data showed a split in acceptance of electronic versus print. The data also show that although humanists may lag behind other disciplines in incorporating e-books into their research, they believe e-book availability and use will increase. . . . The e-book format is appreciated, but scholars may also want the full text along with the print because of the varied types of reading employed by humanities scholars.