When you go to the Pottermore website, you'll see a background with a owl on a table. Maybe this is the owl you'll have to follow? On the website you can watch the video announcement and submit your email if you want to be notified when you can sign up. (I can't submit my email, when I click on the "submit" button, a round loading picture replaces the button but nothing happens) In the right corner there's also some information about the page.
I would lie if I said that I still wasn't excited for this. I'm looking forward to this website and towards getting more information. Although I'm a bit dissapointed that there's going to be more waiting .. And what's this "find out if they're magical" thing? What if there's a sorting hat test when you sign up or something .. ( update: Click the link in the 2nd update, read the article!) Which could be true, since I've found this picture. Have no idea if it's official, but it looks like the "gate" made of paper that opens in the video .. (click on the picture to see a larger version)