Will Google have exclusive control of Public Domain and/or out of print books? I don't see how it is possible. Anyone who wishes can scan PD books and, with permission, scan and post out of print books still protected by copyright.
The copyright owners (publishers and authors) can themselves limit the kind of access made available—anything from those small "glimpses" (images of a portion of a page) to partial content, to complete books.
What remains uncertain is how Google intends to meter books. To really make money, they must limit user access in a particular way, then charge to remove the limit. Someone—an executive at Random House, I believe—suggested that Google levy a small charge for any look inside a book. I expect this will provoke protests from the public, the reaction being that anyone should be able to browse books online, just as in bookstores or libraries. And, really, reading a few pages can help one make an informed decision on a novel or a non-fiction book.