This reminds me of the time God killed a whole lot of Israelites to prevent people from spoiling the 10 Commandments.
Anyone else on earth would kill for an early review from the New York Times. I think Rowling - who I admire a great deal - should not sweat the inevitable interest in the book. People who do not want to be spoiled will not be. The only real way to protect the book's ending is to never release it all.