Geo-tagging Flickr images: the coolest game on (Google) Earth.

It may take a while to get the hang of it, but once you do, geo-tagging is addictive.
It only takes a compatible Nikon camera and a relatively cheap device to all of a sudden find yourself and your images totally Googlearthed.
¿Googlearthed? No way that word exists.
Well maybe it didn’t, but now it does.

Figure this: you connect a GPS device to almost any* Nikon camera and - all of a sudden - the machine knows it's precise location on the planet, instantaneously.
You may not always remember where you have been, but your Nikon surely does.

Now, upload your geotagged stuff to Flickr, hit the MAP button, and there you are.
Even if Flickr links to Yahoo Maps – which is not very cool, nor exactly accurate – you can still get pretty close to where you took the pic. You can readjust this manually, in case the program is too far off.
In case of doubt, I prefer the Hybrid or Satellite view, which – most of the time – makes it easier to fix the camera's position; mainly because it gives you more memorable visual clues.

Of course, if your memory is half decent, you can also get a fix on non-geo-tagged images by navigating around any mapping or satellite based program, especially those which permit earth-bound 3D perspectives – which can be extremely helpful to really nail a location, at times.
You can also do this inside the map application that runs off of Flickr but, frankly, I find that rather cumbersome, and prefer Google Earth for figuring out where a particular shot was taken.
Even then, and especially with older images, it may take some puzzling to sort out where exactly they were taken, especially if the surrounding areas have changed since then.
I also like to shoot from commercial airplanes, and aerials are probably the hardest ones to pin-point.
Anyway, once you figure out where a particular shot was taken, you copy the coordinates, paste them in the Flickr MAP dialogue (and/or in your meta data), and BANG, there you are: geo located…

After finishing geo-tagging your images on your Flickr Photostream, you may want to hit the KML link to the right of the RSS button, at the bottom of your Flickr Photostream page.
This allows you to export your geo-tagging info into a KML file, even though there appears to be a limit on how many geotagged images get registered in it.
This KML file can then be imported into Google Earth. You open GE and import the KML file, after which your geo-tagged Flickr images appear on a Google Earth layer as thumbs which, on clicking, become viewable images (see above) linking back to your Flickr photo stream.
Is that cool, or what?

* Instantaneous geo-tagging is available on select Nikon and Fuji cameras. No other DSLR brand currently offers real-time GPS meta-data writing. Not available on the Nikon D40(X), D60, D70, D80 and D3000.

See also:
Competition for the Nikon GP-1. Promote Systems launch their GPS-D90 for the D90 and D5000
"Geotagging" with your Nikon. Review of the Promote GPS N-1.