iFind is... "MIT's new location-based application for friendspotting", as they describe it (a project coordinated by François Proulx):

iFIND, a project developed at the MIT SENSEable City Lab, aims to improve social networking through some kind of digitally augmented serendipity. Using iFIND, you and your buddies can instantaneously exchange your locations on campus, talk to users nearby, and microcoordinate more effectively. If you are a geek, you will even be able to arrange meetings in real time using the group's center of gravity!

iFIND aims to give full control of location to the users. It is you who can choose, on a peer to peer basis, when to disclose your individual data and to whom.

Technically speaking, it's based on PlaceLab:

Your location is derived from the signals that your laptop's (for example) wireless card detects in its vicinity. Thanks to the high density of WiFi access points on the MIT campus, the software can compute your location accurately (we'd say within a few meters).