Security Week is reporting on a Black Hat presentation by Samy Kamkar titled "How I Met Your Girlfriend".
It finds a visitor's MAC address. It then uses Google Location Services to locate the device.

blackhat http://www.blackhat.com/html/bh-us-10/bh-us-10-briefings.html#Kamkar
Note: Samy Kamkar is known for the Samy Worm.

google cache text of samy.pl/mapxss
http://webcache.googleusercontent.com/search?q=cache:samy.pl/mapxss&strip=1

Security Week http://www.securityweek.com/hacker-uses-xss-and-google-streetview-data-determine-physical-location
Slashdot http://it.slashdot.org/story/10/08/03/0117215/Using-XSS-amp-Google-To-Find-Physical-Location