The Delft University of Technology (TU Delft) in the Netherlands is running TWiki since 2004 at wiki.tudelft.nl.
They created a nice visualization of the evolution of TWiki use from the very beginning, 5 years ago. Each node is a page, links are connections between pages. The graph is laid out using a force-directed algorithm, where the edges (links between pages) pull the nodes (pages) together, and the nodes (pages) repel each other. IgorNikolic and Chris Davis created the visualization and documented the wiki growth over time.
Nice work Igor and Chris!
-- Peter Thoeny