The registration page is very slow right now. I can only imagine that the site is getting hammered with requests. There is more (thanks to Sheila Ruth @Wands and Worlds for the information) at the Guardian
the fresh Potter material – to be unveiled later this year - already stretches to 18,000 words about the novels' characters, places and objects, with more to come. From Professor McGonagall's love for a Muggle as a young woman, to how the Dursleys met (Petunia was working in an office); from new information about Slytherin, Ravenclaw and Hufflepuff houses, to details about wand wood, Rowling's writing will be just one part of the richly interactive, free Pottermore.com website, which is intended to bring the Harry Potter storylines to interactive life for readers.