When Google announced its book deal, they were immediately criticized by many groups and corporations for its potential to give Google too much power over "orphan books".
Orphan books are books where the copyright holder is unknown or the book is out of print. The biggest contention with the agreement is that this would give Google "virtually exclusive license to millions of books".
Because so many groups, including the Department of Justice, have opposed the current agreement, Google is willing to compromise on its deal. The likely result is that Google will be allowed to access and scan the orphan books but will not own the rights to them. This would give competing companies the ability to compete against Google, something that may be impossible if Google had exclusive rights to the orphan books.
A hearing has been setup for October 7th to discuss the necessary changes to the Google book search agreement. It is expected that this review and rework of the agreement will cause for a delay in the rollout of Google's book search.