Do the magnetic stips on hotel room cards contain all your personal details?

I heard that the magnetic strip issued by hotels as a room charge key contains all your personal details including credit card/debit card details . Is this true ? I never hand my room key back when I leave for exactly the reason above it only takes a batch to be thrown out in the trash or a dodgy employee to pass it on to a fraudster,though I must say I dont know if its an urban myth or not. Could anyone confirm either way please?