Forget GPS, Hello WPS
No France writes "A company known as skyhook wireless has announced the commercial availability of its Wi-Fi Positioning System, or WPS. The company has compiled a database of every wireless access point it can find in a given city. When a mobile user running th Skyhook client is in a recorded area, their position is calculated by selecting the surrounding signals and comparing them to the reference database. Currently there are 25 US cities mapped, including New York City, Boston, Chicago, Los Angeles and San Francisco. Apparently this device is accurate to within 20-40 meters, though one has to wonder how well it deals with people moving their wireless access points."
I work for this company, collecting positioning data. Let me tell you, it's a slick setup, and they have a very novel idea for positioning.
Assuming people don't get swap-happy and trade access points all over the place, the reliability should be very high, too.