Why would you not be happy about it, its the same as writing a check and mailing it to Apple and they cashed it, placed your order on back order with an expected ship date. You did want the iPad and pre authorized your card for the charge thereby placing it on pre-order?
People are so used to card companies holding pre authorization, they forget that you shouldn't place the order if the money isn't there, its like writing a bad check.
On the other hand, if your just upset that they are charging your card now, for an iPad 3G to be shipped later, its the same thing as above, a pre-charge hold for merchandise that is being guaranteed to be shipped directly to you. Otherwise cancel the order or never place it in the first place until after it's readily available in stock for immediate shipping.
I was more than happy to place a pre-authorized charge for an iPad, just so I could be sure to have one on launch day. I was charged today about 5:00PM EST, I know this because I set a filter for my online banking to notify me by e- mail when the charge was placed.
Im glad to finally see the charge go through, it was getting nerve racking wondering when they were finally going to do it. But the money was always going to be in my account ready for it, not like I placed the order without having the funds, thats just stupid.