Flickr has about 20 millions geo-tagged photos in its database, meaning millions of tags attached to millions of GPS coordinates. That's a lot, and there is certainly a way to build useful services on top of that.
For instance, Geocodr is a mash-up using Flickr's API to identify the possible location of anything. Type "Eiffel tower" in the entry box, and you get the exact location of the famous French monument. Type "Celine Dion", and you get Las Vegas.
But Yahoo! is taking it seriously with it's prototype : Zurfer. It's a mobile location-based photo browser. With Zurfer, you will access your Flickr pictures and browse the entire database of pictures taken around your current location. You therefore access user-generated geolocalized content from your phone.