You wouldn't trust $100K worth of data to 40-bit encryption authentication would you? So how about your automobile? It looks like stealing a high-end car using a laptop isn't very difficult to do.

Robert Vamosi has written an article on keyless ignition systems based on a study from Johns Hopkins University and RSA. Vamosi notes in the conclusion of his article that the manufacturers of the RFID systems don't seem think there's a problem. So get yourself a tin foil cover for your key! It's an interesting read, check it out here.