Mentioned this in the big app store thread but thought it was worth highlighting. I shop using the "Shopping Cart" iTunes preference. In the App Store clicking "Buy App" does not use the shopping cart, once you hit that button there's no going back! I like the Shopping Cart method because I can browse around adding stuff to the cart without committing to purchase, then when I'm done I can review what I've chosen and if I'm spending too much I can take something out. Quite a huge oversight if you ask me.