A good source for info on them is www.slashdot.org
You can search the older archives for RFID related articles. They have a link to one in today's stories too.
There's been a lot of coverage of RFID among privacy advocate sites because once it's widespread you could practically track a person where ever they go.
There are even sites on how to disable the chips woven into clothing or other items. Pop 'em in the microwave for 10 seconds and fry the transceiver