That is just ---smurfing--- sweet.
Imagine leveraging GPS and free WiFi hotspots to download the virtual graffiti. With a portable laptop/PDA/cell/whatever and a pair of virtual glasses, imagine a whole other virtual world hidden on the streets of a major city.
There was a Digg article a long time ago where someone created a false electrical wall socket box that plugs into an outdoor wall socket. It had a passthru for powering whatever is plugged in but it had additional circuitry powered by the 112v line. Imagine setting up markers with wireless downloadable graffiti.
