Of one of my favourite iPhone apps demoed today at WWDC was Sense Networks' Citysense (even though it's already been on show on Blackberry during June).

Citysense analyzes massive amounts of aggregate, anonymous location data in real-time. Macrosense is already being used by business people for things like selecting store locations and understanding retail demand. Citysense, on the other hand, provides live heatmaps of the city that show whether the city is busier than normal and where there are unusually high levels of activity. Could be useful if you're in Melbourne and considering moving nightspots before the 2am lockout. Or if you're visiting a place for the first time it would be great to see where people with similar tastes as yourself are hanging out.

Citysense is really just a test for Sense Networks in trying to see what kinds of consumer-facing applications might take advantage of their network (they term this one "Nightlife enhancing"). Although some people may not feel comfortable about having their movements tracked across the city, it's fascinating to think of what this could offer (as they say) anonymously - mood by location, length of visitation (urban stickiness) or mob-based street games. This capability is not really all that new but iPhone mania may offer enough installs to make the data interesting.