The Pottermore blog has been updated with a few questions and answers sent to them by fans. Read all the answers here and a select few below:

Can you please explain what you mean by ‘online reading experience’? How much will I, as a Pottermore user, be able to affect the story? After all, hasn’t Harry’s story already been told?
The best way to think of Pottermore is as an interactive, illustrated companion to the books. J.K. Rowling wanted to create a site where her stories could live on and where readers could explore them in a new way. In addition to discovering new material from J.K. Rowling about Harry’s world, you’ll be able to interact with key story Moments (the Sorting Hat sequence, for example) and upload your own comments, thoughts and artwork for all the characters, objects and places that you come across.

Once I’ve been sorted, will I be able to change houses?
J.K. Rowling has created a series of questions for the Sorting Hat, and how you answer these questions will determine which of the four houses you’ll be in. Once you’ve been sorted, you won’t be able to change; the Sorting Hat’s decision is final!