The paper, “Automatic Construction of Travel Itineraries using Social Breadcrumbs” (PDF), cleverly uses the data often embedded in Flickr photos (e.g. timestamp, tags, sometimes GPS) to produce trails of where people have been in their travels. Then, they combine all those past trails to generate high quality itineraries for future tourists that tell them what to see, where to go, how long to expect to spend at each sight, and how long to allow for travel times between the sights.