So, there has been some recent press about how people can now be tracked via the Nike+ iPod sensor, which of course broadcasts a unique identifier for a distance of up to 60 feet. Although there is no uniquely personal
information broadcast (ie, your name
is not embedded in the sensor), each sensor does
have a unique ID that can be tracked.
Of course, the person doing the tracking would have to be within about 60 feet of you, and would have to be able to associate the sensor's unique RFID with your actual identity.
More info can be found at the following links:
Personally, I'm not too concerned....