I was looking into RFID a bit deeper, and came across a very interesting security video by Chris Paget:
Here's a fun bit for you (or scary) cued up:
The cued part there talks about mall surveillance and how you can track people.
He demonstrates reading RFID up to 217 feet (with equipment you can buy on ebay) and illustrates how RFID can be read up to 317 MILES away in theory.
For those unfamiliar with this stuff, you can effectively steal credit cards, clone epassports, clone IDs, clone keycards, tell what colour underwear people are wearing, find out all kinds of information that you really shouldn't.