The Pottermore Insider Blog has been updated to let fans know that Beta testing for those million fans who signed up has begun! They will be staggering the entrance to the site so you still may not get your email for a few weeks. According to the entry:

As Pottermore Beta users, you’ll be exploring all the different elements of the site and, hopefully, sharing your thoughts with us along the way. How? By using the ‘Beta feedback’ button. You’ll find it located at the bottom right-hand corner of every page on the site […]

It’s important for us to know what you enjoy about the site, what you would like to see improved, and that you tell us about any parts you think aren’t working smoothly. As well as the ‘Beta feedback’ button on the site itself, we’ll also send each Beta user a survey to complete, asking some detailed questions about the Pottermore website.

All this information will be collated and analysed to help make Pottermore as enjoyable, interesting and easy-to-use as possible.

They have also posted some information about registering for the official opening in October.

• If you have submitted your email address to be notified when registration is open to all, then you’ll be hearing from us soon, and you’ll be able to register for entry in October.
• If you asked to be notified when registration was open to all but also registered for Beta, then you may receive two emails from us. You do not have to register for October if you already have a validated early access (Beta) account. In other words, if you received a Beta ‘Congratulations!’ message then you can ignore the ‘Pottermore registration is now open’ email (although do feel free to forward it to your friends!).