Greg just pointed out an interesting looking paper to me. Authored by Jure Leskovec and Eric Horvitz at CMU/MSR respectively. World Wide Buzz: Planetary-scale Views on an Instant Messaging Network looks at the nature of IMing by mining a huge volume of data: 30 billion conversations. Among the interesting views of this data is that below, which uses a heatmap metaphor to indicate the most active lines of communication. A line is drawn between the locations of the participants in the converstions. When a line crosses a cell it increases its value (red).