Flickr allows you to geotag your photos. You need to go to Organize mode, click on the map, choose a location and drag the photos to that location. Flickr uses Yahoo Maps, that are less detailed than Google Maps, especially outside of the US. By default, the location of the photo will be available to anyone, but you can change that for all your photos or on a case by case basis.
Flickr should also try to guess the address from the tags or from the title, as most people write the location there. But in the future most cameras will have GPS or they'll be integrated with a system like Sony's GPS-CS1, "a 3.5 inch long GPS device that will add geographic data to pictures taken with your Sony digicam".
Flickr has created a screencast to explain how to use the new feature.
To see all the photos that have been geotagged, visit this map.
Related:
Picasa 2.5 allows you to geotag photos in Google Earth
Panoramio - geotag photos in Google Maps
