When you go to a conference, there are typically several talks going on at the same time, and you can always tell there's a popular paper coming up when you see people leave a bunch of rooms at once and head straight into one. There's also the unfortunate case when someone speaks, and there's only a handful of people in the room, all in the back staring at their laptops. Open Data City visualized this activity during the German internet conference re: publica.
Open Data City used MAC addresses and access point connections to keep track of where devices went. So a person might be in a room connected to the nearest access point, disconnects as he leaves, and then reconnects as he reenters another room, which provides the flow.
It's fun to watch the conference play out even if you didn't attend. Each dot represents an attendee, and as the animation plays the dots migrate from room to room. Click and drag over the dots to select specific people. [Thanks, Michael]