The Authors Guild believes that Google should only scan books belonging to writers that opt in (yeah, right -- and your VCR should only record shows from broadcasters that opt in, and Google should only index web-sites that opt in). An opt-out system such as the one that Google has proposed isn't good enough for the copyright nihilists at the Authors' Guild, who believe that even though the Google Print program will sell more books, it shouldn't be allowed without permission from rightsholders.
But the Authors' Guild has brought a class action suit on behalf of all writers who will be scanned by Google Print. That includes me, Siva Vaidhyanathan, Larry Lessig, and innumerable other authors who think that the AG is full of crap. In other words, the AG believes that Google shouldn't be allowed to opt writers in to its Google Print program (which will make money for writers and sell more books), but they believe that they should be able to opt writers into their costly, suicidal lawsuit against Google, which, if they are victorious, will reduce sales and take money out of writers' pockets.
The Authors' Guild represents a few thousand writers, an insignificant fraction of the writers whose works Google proposes to scan. They don't speak for me.
Hell, if I was in charge of auctorial response to Google Print, I would direct the use of Authors' Guild funds to purchase and deliver a fruit basket every single day to the Google Print project office (with a second basket to be delivered to Jeff Bezos for Amazon's Look Inside the Book) by way of thanks for the excellent work they are doing to promote books. Link
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.