I recommend anyone who's planning to prepare for the SAT purchase The Official SAT Study Guide (you'll see me refer to it a lot on this site simply as the Blue Book), but that doesn't mean I think it's the world's greatest prep book. In fact, I find the whole first half of it to be pretty weak.
It makes sense that it would be, if you think about it. The College Board wants to sell books, but at the same time prop up their test as the go-to exam for college admissions. They can't very well sell you a book that's going to reveal every strategy necessary to ace the test, they'd be putting themselves out of business. So they sell you a book full of very good practice tests, and very mediocre strategies.
They know that the back cover of their book (you'll see it when you buy it - it insists that there are no tricks to help you get a better score) is baloney. They know that the first half of the book isn't that helpful. But they need to prop up the myth that their exam is a pure measure of your academic prowess. They can't very well admit that it's susceptible to test-specific strategies and tricks, and that kids who prep with someone who knows them have a huge advantage!
So buy the book, and do ALL the tests. They're written by the same people who write the SAT, and in fact the first three tests in the 2nd edition were real SATs (they're the October 2006, January 2007, and May 2007 (Saturday version) tests, respectively). But don't take the back cover, or the first half of the book, too seriously.