Harry Potter fans, many in costume - mostly wizards, witches and Hogwarts pupils, but I saw one broomstick and one Hogwarts castle too! - had come along from all over the UK, Europe, USA and Australia to queue up for hours outside a bookshop on a chilly night in central London to buy a book. And this wasn't even a signing - J K Rowling was doing a small, exclusive event somewhere else. Some of them starting queueing three days before!
The atmosphere was excellent and although there was some entertainment, the fans queuing generated all the excitement themselves. Whatever you think of the books (and I like them - I'm half way through Deathly Hallows already), I can't think of any other book or series of books that could inspire this kind of enthusiasm and passion.