There are over 35 million geotagged, time-stamped photos on flickr now. That's enough to start doing some pretty interesting analyses, including this one from Crandall, et al., at Cornell (presented at the WWW 2009 conference, "Mapping the World's Photos" [PDF]). Not only is it possible to map hot spots of world tourism, but by incorporating the time stamps to map the routes people are taking, you can make out individual streets. As suggested by the Information Aesthetics blog, you could even design popular walking tours.
Once GPS-enabled cameras represent a larger share of the market, flickr may provide data for all sorts of important analyses: tracking SOD, the migration of an endangered song bird, or estimating the "desolation" of a place: the world heat map that the Cornell group presents looks shockingly like the lights at night. The machine... it's ALIVE!!!