well, it could be simple. two approaches:

a) write a front end for a popular dating site and somehow connect your profile there with gps data

b) define an extension to xmpp that describes your sexual preferences and use the existing xep-0080 to broadcast your location

instead of using gps for positioning, one could also publish the unique bluetooth adress of the phone. this would help finding people in clubs where gps usually doesn't work very well.

i like the idea. no matter which approach, the application could work on several plattforms.