They can steal your smartcard, lift your passport, jack your car, even clone the chip in your arm. And you won't feel a thing. 5 tales from the RFID-hacking underground. (The section about cloning the chip in your arm can be found at page 3 in this article below.)
 
FULL STORY at
http://www.wired.com/wired/archive/14.05/rfid.html