Harry Potter has been touted again and again as the next big thing in getting kids to read, and JK Rowling is certainly not arguing with this. The cracks are beginning to show in the evidence though, as the early readers of Harry Potter get older and haven't the time nor the inclination to read the books. People are even beginning to admit, sacrilege of sacrileges, that they are no longer enjoying the books.
Despite the intense and wide-ranging following the books have, it simply is not reasonable to expect one series of books, often released more than a year apart to really make a difference to children's reading habits, just as it is not really reasonable to expect one bad computer game or TV show to put children off. The biggest reason why Harry Potter isn't going to make a difference to children reading, though, is that each of the books is being made into a movie, and each movie is more feature packed than the last. For most kids, the movie will be enough, I would think, and the book will be irrelevant.