This article from 2003 details the Stanford University digitization program, where they are using a Swiss scanner that can do up to 1200 book pages per hour. The article notes that a 200 page book can be digitized in 20 minutes.
Stanford is now working with Google. In this more recent interview, Keller notes that "The Google plan allows us to accelerate our digitization schemes by orders of magnitude." The interview notes that the books will be digitized at Google's Mountain View, CA headquarters, which means that the books will be unavailable for some period of time.