Naomi Eichenlaub has published "Checking In With Google Books, HathiTrust, and the DPLA" in Computers in Libraries.
Here's an excerpt:
Google Books and HathiTrust have been making headlines in the library world and beyond for years now, while a new player, the Digital Public Library of America (DPLA), has only recently entered the scene. This article will provide a "state of the environment" update for these digital library projects including project history and background. It will also examine some challenges common to all three projects including copyright, orphan works, metadata, and quality issues.