I attended the latest seminar (5th) on this settlement held by Access Copyright on February 19th, 09. Roannie Levy from Access did an admirably clear job of walking approximately 300 creators through the complexities of this agreement but was careful not to speak for or against it. She would say only that in the U.S. both writers and publishers have said YES to this settlement.
I recommend you visit the Google Settlement home page (see Useful Links page) and read its explanation. Access has also posted its seminar online with commentary and is running still more seminars in March. Unless you love poring over these sorts of documents, it’s easier to bite a few hours and take their seminar than try to digest the implications of this settlement on your own.