At the LODLAM conference, Roy Tennant said that OCLC will be releasing the bibliographic info about the top million most popular books. It will be released in a linked data format, under an Open Database license. This is a very useful move, although we need to know what the license is. We can hope that it does not require attribution, and does not come with any further license restrictions. But Roy was talking in the course of a timed two-minute talk, so he didn't have a lot of time for details.
[NOTE added June 6] The OCLC has clarified Roy's remarks here.