I just noticed that my charge is gone as well! I haven't had that happen in any pre-orders. The actual order still just says preparing for shipping, but my logical side is telling it will be okay, because its not in the processing phase, but my un-logical side is cringing.
I haven't preordered from Apple until this time around, but with AT&T; however, every year my pending charge always fell off on Tuesday until it had actually shipped. Every year it caused panic, and then all would be well when it was delivered on launch day.