Microsoft released its own book search service, that includes only out-of-copyright books and books for each Microsoft received permission. The approach is different from Google's initiative, where publishers can only opt-out from Google Book Search.
But the most interesting thing about this release is a statement from Danielle Tiedt, general manager at Microsoft: "As we move out of beta, what you will see is that book content integrated with the Web content (search results on Windows Live Search). What we are focusing more of our efforts on for live searching is integrating all of those content types together to give you the most relevant results. Sometimes the most relevant will be from books. If, for example, it's a search on historical content, chances are the most authoritative content may be found in books."
It will be very interesting to see books as search results, and mixing various content sources is something that Google intends to do with Google Universal Search or SearchMash.