The New Yorker and IBM used data from New York City's new bike share, Citi Bike, to create an interactive map that shows how much use the system is getting. They can't track bikes around directly with GPS, but they know when a bike is docked at a certain station, when it's out, and where it ends up being docked again, so that gives a pretty good idea of the ebb and flow of bikes around the city.
You can see the interactive map here.
If you run the recorded timeline from beginning to end, you'll notice some pretty big changes in the usage patterns over time, which is normal for a new service; people have to sign up first and figure out how to integrate the bikes into their transportation routine. It will be interesting to revisit this map in a year to see how much it has changed.
Via New Yorker