I figured as much... still, it never hurts to ask second opinions. I have not had trouble with magnets and my cards before in any circumstance... and it does seem like you need special equipment to demagnetize something, as we have special gear at the library (one of two jobs) to do such tasks... and even when I used to work retail, there was special equipment to demagnetize security strips and all that junk. So, I was under the impression that the magnet closures on the sporran would pose no threat.

As a side note: Mythbusters is a fun show, I don't get to catch it often enough.