This is slightly old news now, but these maps by Eric Fischer are absolutely stunning. They map out the locations in cities where photos on Flickr and Picasa were taken/geotagged. The differently coloured lines indicate modes of transportation that the photographers took: Walking (black), cycling (red), and moving in a motor vehicle (blue).
As someone who does quite a bit of design work and also works with research data fairly often, I adore data visualizations, especially when they are beautiful enough to stand as works of art in their own right. The last two images are maps of Toronto, with the left image mapping out modes of transportation and the right image mapping out photos taken by locals (blue) and tourists (red).