There's been a lot of talk about the injunction brought to prevent a discussion at Defcon about hacking in to RFID card-based transport systems, which has implications for a number of cities around the world.
According to a rather less than complimentary piece about RFID in Fierce CIO, there is an RFID vulnerability assessment report which talks about the problems with the Massachusetts Bay Transportation Authority (MBTA) systems.
You can view the article here and the vulnerability assessment here