Wow, this is really cool. It won't really enable person-to-person transfers, but person-to-POS in a mobile format is slick. I'm a liiiiiiitle bit leery of having someone punch in all of my card data to their iPhone. It would be a bit too easy to hold on to those numbers for too long. But then, I'm fooling myself if I think that those sorts of things don't happen with standard card readers as well.
Mobile handheld card processing will be fantastic for a lot of small businesses.