Cool, I speculated on this a couple of months ago in my blog (although even then it was already fairly predictable). http://blog.blinker.net/2008/04/15/exploring-geotags/

Another application could be to monitor the spreading of plants and animals, or other memes (fashion sense, cars, etc.).

When I wrote the blog article, it was difficult to get GeoTag information out of flickr (no search option for "images with GeoTags"). Anyway, I wish more data was freely accessible...