In "Reading Bad News Between the Lines of Google Book Search" (Chronicle of Higher Education subscription required), Peter Brantley, Executive Director of the Digital Library Federation, discusses his concerns about Google Book Search.
Here's an excerpt:
Q. Why are you concerned about Google Book Search?
A. The quality of the book scans is not consistently high. The algorithm Google uses to return search results is opaque. Then there's the commercial aspect. Google will attempt to find ways to make money off the service.