The card has the ability to change and use a different number for each transaction. You can also store multiple accounts on one card. From Ars Technica, “The secret lies in the company's innovative magnetic strip, which can be programmed in real time, and—more importantly—wiped clean just as quickly.” The card looks and acts pretty much like the credit cards you have now, but instead of embossed numbers, this one has an LCD screen. The screen shows you a different number for each purchase and has to be unlocked, by tapping out a code, before each transaction. Again from Ars Technica: “Once the transaction is over, the numbers leaves the face of the card, and the magnetic strip returns to its blank state.” Citibank has already started using the cards in a pilot program.
You may see this as the natural progression of technology, and my logical mind agrees, but part of me just had to supress a yelp of “Ohhhhh, maaaagic!”