As a huuuge fan of Harry Potter I had to sign up to be one of the beta users of Pottermore. I recently got my acceptance email!
It's been fun, but there's not much to do there once you've gone through the first book, apart from brewing a few potions and learning a few spells. I was fairly disappointed at the lack of interaction and the fact that house common rooms were nothing but noticeboards, but overall the graphics are great and it's a fun way to kill time, at least for a few days.
I was sorted into Slytherin which was not at all surprising! I've known for ages that I'm a Slytherin, so I'm very pleased. My husband's a Gryffindor.
This is a screenshot of the gateway. It displays the journey through the books. Only the first book is active right now. Each node is a chapter, and the tiny avatar squares show the progress of people you 'friend' who are currently online. User names are automatically generated for people when they register (mine is FlightDraconis122) but if you 'friend' someone you know, you can add a nickname so that you remember who they are.
For those of you who haven't heard of Pottermore or haven't gained access to it:
Each important moment in the first Harry Potter book is illustrated, and objects are hidden in the illustrations to collect and store in a trunk -- things like chocolate frog cards, books, galleons (these are added to your Gringott's vault automatically) and potion ingredients. A lot of the chapters include J.K. Rowling's explanations behind names as well as background stories of certain characters, details we don't get to see in the books. Those are quite interesting and inspirational!
As you move from chapter to chapter, you get to do the things Harry did, including buying a wand at Diagon Alley and getting sorted into a house at Hogwart's. Once you've gone through all of the chapters, you can brew potions to gain house points, or you can practice spells so that you can eventually challenge people to wizard's duels -- for now, the duel option is disabled. They're probably working on it.
Overall it's pretty fun, but I feel once the novelty wears off I won't visit it much due to lack of activities. I've heard the second book is scheduled to come out only in 2012, which is disappointing. I'm not sure what we're supposed to do till then. :P