Pottermore isn't a new book. It's a website, and basically the announcement is that JK Rowling is going to finally offer e-book versions of the Harry Potter Series. JK Rowling had always refused to publish her books in e-book format, in part to discourage piracy, but of course, all of her books have been pirated for years, and in fact, she is probably the most pirated author of all time because of that fact.
The website has very little content right now. I guess I was hoping for something more exciting. I'll admit it-- I'm sad it isn't a new book.
You can sign up for alerts, but they aren't even taking e-mail sign ups yet, because of "overwhelming demand." I don't know how you can have "overwhelming demand" when no one is actually signing up for anything yet, but then again, I'm not a marketing guru. I'll post more news when I hear something new.