Ah, the Sidekick 3, with its IMing, emailing, texting and credit card erasing capabilities. Wait, credit card erasing?
A couple guys started experimenting with the SK3 once they found a pen sticking to it when they removed the former from a bag. They went on to find that the magnetic latch that allows the SK to do the "cool flippy thing" is really powerful. When open, it can hold up a regular table knife. When closed, it's still able to hold up a fork.
So what does this do to that credit card sitting next to the Sidekick in your pocket? It obliterates the stored data. These guys took an expired card and ran it through a terminal to test whether it was recognized—it was. After sticking the card up next to the closed SK3's magnet, subsequent swipes produced absolutely nothing on the terminal. It wasn't even recognized as a valid card.
Someone ought to go try this with the card inside of a wallet and see how thick of a wallet is necessary to protect your cards, driver's licenses and badges. For now, you may want to keep them in separate pockets.
Sidekick 3 Warning: Sidekick 3's Magnet Will Erase Your Credit Card in Under a Second [The Internet Patrol - Thanks Phil!]