Is it true that hotel card keys hold personal data and should be retained by the customer and destroyed? Name withheld
It's a lovely story and dates back to an erroneous press release from the police in Pasadena, California, in October 2003. It's false, and you can read the police's retraction.
The story is covered on urban legends site Snopes (http://www.snopes.com/crime/warnings/hotelkey.asp), but will no doubt circulate for a few more years.