After seeing Cooper Smith's visualizations of data from runners in New York City, I wanted to see what similar data sets would look like for other cities. Nike+ doesn't have public GPS logs, but MapMyRun does, if you are willing to spend several hours clicking through search results to hit the "Download" buttons, so that's what I did to get the tracks for these 771 runs (from June 13 through August 9) in San Francisco.
As Open Source Planning has pointed out, uploaded runs come from a fairly small, self-selected group of people, the most obvious result of which is the total absence of the southeastern corner of the city from this map. It is also a very self-conscious process, so it is biased toward intentional, and often intentionally difficult, trips made for their own sake, and away from the repetitive patterns of everyday life.
Unfortunately the MapMyRun tracklogs do not have date and time stamps, so it is not possible to do the time of day, pace, and interruption analyses that Cooper Smith did. I should have done direction of travel, though.