http://www.whynot.net/view_idea?id=1023
RFID tags are tiny radio responders that can be attached to anything for inventory, theft prevention and other purposes. They work in the same manner as devices like “EZPass” and "SpeedPass" that allow you pay tolls and buy gasoline without any interaction. A radio signal transmitted nearby provides the energy, and the transponder responds by echoing out a serial number in a radio response.The miniature tag versions are just now starting to work their way into the economy. Recently Michelin announced that soon every tire they make will have an RFID tag, and Gillette signed a contract to buy millions of the tags.
Many people fear that with little automated inventory tags on everything, our privacy could be invaded in new and insidious ways. The theory is that you could be surreptitiously scanned in many public places, and the RFID codes from your clothing and personal belongings could be used to track you. Some stores have promised to erase the tags somehow at the checkout so they cannot be used that way, but how can we be sure?