My 11 yo nephew was wide-eyed as he dramatically told me how it was "proven" that the elf moved, etc.  After that, I couldn't not buy it for him for Christmas.  He was so excited when he opened it!  I read through the book (which I thought was pretty goofy, but if the kids like it, then who am I to judge?) and it at least explained the whole concept.  I know many people think that this elf idea is creepy, but I have seen so many who have had fun with it, too.  It seemed to be well made, and the boxed-set made it a wonderful presentation for gift-giving.