I just came across the Citysense application for Blackberry which allows participating users to monitor active areas of the city (only San Francisco at this time) through real time network monitoring. Citysense is powered by Sense Networks application over the GSM networks. There also appears to allow personalization of the system to attribute personal tastes to the city search, creating an opportunity to find like minded people. I blogged this because because I think this is a very exciting way to bring impromptu social interaction to the streets.