You should read Bruce Sterling's post on (a book about) the possible misuse of RFID chips. If you've been keeping up with RFID news, the new version of the American passport is slated to have one of these chips imbedded into it, and there has allegedly been little thought given to security issues that will arise from their use (like identity theft and data mining). Don't know what I'm talking about? You should find out.
Thanks!