Simson Garfinkel of MIT Enterprise Technology explains:

RFID technology is already broadly deployed within the United States. Between the “proximity cards” that are used to unlock many office doors and the automobile “immobilizer chips” that are built into many modern car keys, roughly 40 million Americans carry some form of RFID device in their pocket every day. I have two: last year MIT started putting RFID proximity chips into the school’s identity cards, and there is a Phillips immobilizer chip inside the black case of my Honda Pilot car keys.

He comes to an interesting conclusion:

The problem of voluntary, industry-approved privacy standards is that they’re voluntary—companies don’t need to comply with them. And the very real danger facing the RFID industry is that a suspicious public will push for regulation of this technology. Although the industry has successfully killed legislation proposed earlier this year in California and Massachusetts, high-handed actions on the part of RFID-advocates will likely empower consumer activists and their legislative allies to pass some truly stifling legislation.

Indeed.