RFID & Loyalty Cards

I learned reading this article in the RIFD journal that carrying a RFID-tagged loyalty cards would "enabl[e] store staff to know who walks in the door so they can shout out a welcome" to me. Frankly, this does not appeal to me, not that I am not a friendly person, mind you, but because of some pesky privacy concerns. So, the data contained in the card would be personal information. Would my credit card information would also be stored? Could the data be read by any reader, so that any owner of a RFID reader would be able to read my info, including, oh dear, my dress size?