Old news from Gizmodo and Wi-Fi Networking News (quoting WiFi NN):
Skyhook has assembled a database of information about 1.5 million access points across 25 major cities in the U.S. by driving every street in every city. Their software records multiple data points per sample for directionality. Fire up their software on a laptop, and it compares the Wi-Fi information it sees with what’s in the Skyhook database, popping out a latitude and longitude within 20 to 40 meters.
Also geolocation related: Monopoly Live: London style.