I was reading up on a demonstration by Samy Kamkar on his web site where he accesses a database created by Google to map the MAC addresses (electronic hardware serial number) of wireless routers. Part of the data may have been collected by the infamous camera cars used to create Google's street view. Samy's contention is that every Android phone harvests the GPS position and the MAC address of every wireless router they pass by in the street. That information is then transmitted back to Google where it is used to update the database. On Samy's web site you can enter the MAC address of your own wireless router and get a response which shows the location of your building. It was accurate to within 50 metres for my building.
No doubt similar data will be gathered for the iphone population as well. Soon (now) advertisers and security forces will have access to a database where they know the physical location of every wireless router in the country. Snooperville is definitely here! As you walk or drive past a "known" wireless router your journey will be accurately tracked. That information can be tied into CCTV cameras which film your face or vehicle.
I'm currently working on a storyline for my next book where the bad guys use the MAC address of the victim's smartphone to track the good guys. This would be highly accurate and leave no trace on official records. I'm envisaging a business where couriers/messengers are paid to carry the smartphones of rich people to leave a false trail of tracking information.