That could certainly make things very interesting... I myself encountered an issue like that with my local telecom(thought they'd already charged me, but they hadn't, had to get a new CC#, ended up getting billed 2 months at the same time by the time I got everything straightened out).
While I appreciate the concept of this attempt at customer friendliness, when I pre-order something I want the money to be GONE so that I can't accidentally spend it on something else. This is the entire reason I pre-order, not to ensure I have a copy(because I know I can get one eventually, somehow, even if I have to wait a week or so), but to ensure that I have it paid for and no longer have to factor it in to any kind of thought processes in the future.
I'm also going to agree with the gentleman that said its much, much better to be blizzard than valve in the release date situation. A "Its done when its done" approach with a guesstimate(and make sure its VERY CLEAR that its a guesstimate) as to the month that its going to be released is far preferable to the "Its coming out xx/xx/xx" and then going "Well, we know we SAID it was coming out xx/xx/xx, but now its not, we'll let you know when we feel like having you play the "are we lying to you again" game in a little while."
Good news about the additional beta testing, very, very poor way/time to announce it .