Pottermore.com will be a place to access digital audiobooks and, for the first time ever, e-books. People will be able to participate on the site and she'll be chiming in with new information about the books and the world that she's been holding on to for years.
Pottermore.com will be open to everyone in October, but a few lucky people will get to see it early. She advises you to follow the owl.
Update: I got the page to load. You can submit your email and you'll be a notice when the site is open in October. But you can also come back on July 31, Harry Potter's birthday and find out how you might be able to get in early.
I think it's much better than an online game, which is what many people were suggesting. I do suspect that there will be game-like qualities about the site like she's used on her personal website.
I do wish it was a new book but I can be content with this.
Update: Leaky is updating their site from the press conference. Rowling will be launching the site with 18,000 words from her, which is reportedly about 1/3 of what she's written. Exciting! Also those beta users on July 31? There will be 1 million of them.