These following web services are good examples of interoperability of geo-data.
Example of an overlaid on google maps based on crowdsourcing the number of geotagged Panoramio photos (owned by Google in July 2007).
Example of a heatmap overlaid on Google Maps, based on crowdsourcing (the number of Panoramio photos taken at each place in the world).
and if you click on "see more"
panoramio, google streetview, wikipedia, tripadvisor research, and google search.