In my full time job we do a lot of work with magnetic strips and barcodes. I have access to a magnetic strip reader and EVERY slot card or room key I've looked at never contained any personal information what so ever. The slot cards generally only contain your player# and maybe your name. All of the information is normally stored on their servers and they use the player# to reference that information as needed. Room keys rarely have anything useful on them at all. Of course there may be exceptions but I don't think it's anything to worry about. As mentioned before, swiping the magnetic strip with a strong magnet will normally destroy anything that is recorded if it's of any concern.