Interesting paper (PDF) on RFID security (or contactless smartcards).  The author states that the security of both contactless and contact cards is the same, "however, some attacks [against contactless cards] are inherently facilitated."

This is going to be an issue with the new RFID passports, that not only the US but all other major countries are rolling out.  It's also going to be an issue as RFID chips are being embedded in credit cards.