The fine folks at Intel's Berkeley Research Lab are deploying a mobile phone application, Jabberwocky, to investigate "familiar strangers", as part of the Urban Atmospheres project.
I haven't quite parsed what the purpose of the project is, other than to study the relationship we have with folks we regularly encounter, but never interact with. But Eric Paulos, a former neighbor in Soda Hall, is part of the team, and that guy has some chops.