I guess it's how it's used
If Google just uses it as some kind of index "Book X by Y, ISBN N contains what you are looking for" and maybe with a highlighted paragraph or something, then I totally fail to see the issue.
If, however, Google vomits up the entire book or sells/provides by any means a copy (or large portion) of the book for which the publisher receives no remuneration, then that is an issue.
And looking at Google Books it appears to be the former, so I am not sure what their problem is as Google Books just lets people find their book and then easily buy it. Surely that's of advantage to the publisher?


