http://www.newscientist.com/article/dn20336-internet-probe-can-track-you-down-to-within-690-metres.html
"The new method zooms in through three stages to locate a target computer. The first stage measures the time it takes to send a data packet to the target and converts it into a distance – a common geolocation technique that narrows the target's possible location to a radius of around 200 kilometres.
Wang and colleagues then send data packets to the known Google Maps landmark servers in this large area to find which routers they pass through. When a landmark machine and the target computer have shared a router, the researchers can compare how long a packet takes to reach each machine from the router; converted into an estimate of distance, this time difference narrows the search down further. "We shrink the size of the area where the target potentially is," explains Wang."