June was a great month for booksellers. Oprah restarted her book club, Hillary bared her soul and, best of all, Harry Potter and the Order of the Phoenix surprised even the most optimistic pundits. What with book sales down as much as 5 percent last year, booksellers are ebullient. Whose second-quarter sales will see the biggest impact? Barnes & Noble, at least when it comes to Harry, according to a JP Morgan survey of sixth and seventh graders. Of the 84 percent who said they planned to buy the book, almost half said they will buy it at Barnes & Noble.