I think they also have a 30 days price protection guarantee that takes into effect from the day your item is shipped. It's not automatic afaik, you'll have to check the price listing and file the request manually if this happens.
'I meant to say 'cheapest the item was ever listed at when it ships as long as you pre-ordered it and the price goes down'
Whenever you pre-order a book, CD, video, DVD, video game, or software item, the price we charge when we ship it to you will be the lowest price offered by Amazon.com between the time you place your order and the release date.