"I think it is a great idea. As other commenters have mentioned, there are several hurdles to clear to gain widespread acceptance. My main concern would probably be reliability of the cards. Electronics in cards can have a tendency to break when bent. Fortunately, they will only get better. I would hate to be in a money-critical situation, and when I go to pay and it won't function. You could be at dinner with your largest potential client, or arriving at the only service station for 250 miles in any direction, your phone doesn't have a signal, there are no payphones and the proprietor's phone isn't working when your card fails. Even though I am a rabid early adopter, I would wait awhile before getting one of these cards, to make sure they are robust (or at the very least carry a backup card)." - Seth Greenblatt