The credit card concept is mainly based on trust at the moment, and assumes that most people are honest - the actual security involved at the moment is shockingly bad. I’m often bothered by how little attention is paid to signatures by shop staff, and this experiment proves it.
Discussions on the UK Crypto list at the moment make me doubt that the new PIN based cards will be much of an improvement. Storing the password on the card seems a potential problem - the encryption will be broken.
Link: The Credit Card Prank