Anybody ever used Mobile Speedpass? That's RFID.
I don't understand why anybody is calling this a "tracking device." With a six or eight inch diameter antenna on your RFID reader, you're lucky to be able to read the darn things at a distance of six inches. So, as long as the person you're trying to track is within six inches of your RFID reader, I guess you can track them.
I also hear people calling them "Spy Chips." Evil corporations are going to stick them in your clothing, and somehow know you're every move. Heck, if you're worried about an RFID chip in your shirt, throw your shirt in the microwave for 15 seconds, and that will take care of the chip for good.
At least for positively identifying a person, biometrics (iris scan, retina scan, fingerprint scan) is about the only way you can positively identify a person.
I guess about the only thing good about implanting people with these chips, is that it's a lot harder to accidently lose a chip that's implanted in your arm, than to lose a flimsy little ID card with an optical or magnetic strip on the back of it.
-Tinytoad