I need to make an important factual correction to the above.
The settlement is NOT "opt out" where in-print books are concerned. Google cannot display ANY part of a book that is commercially available without FIRST getting permission from the publisher and author. Even where Le Guin is distributing her own e-book of an older work for $1, it is considered in print for purposes of the settlement; thus, she does not have to opt out. She may not understand this important point.
The only books that Google may use on an opt-out basis are out-of-print books. Since there is, by definition, no current market for those books, I feel that authors have nothing to worry about here. If they start getting money through the Google program, and they don't like it, they can always opt out.