Interesting article I found on Boing Boing about blue-tooth mobile phones that recognized other blue-tooth enabled devices around them and keep track of their IDs, eventually building a list of “familiar strangers” or people who are often in your immediate area.
“It’s based on the research of a brilliant Yale psychologist named Stanley Milgram, who died in 1984. One of the many remarkable ideas Milgram came up with was that of the “familiar stranger.” These are people that you see in public on a regular basis, but do not talk to or otherwise communicate with, at least not in any normal sense.”