I got a handheld GPS device in early 2009 and keep it in my camera bag, so all my photos in the last ten years are geotagged. At the beginning of this year I started migrating all 15 years of my photos to a modern hosting platform. I made the, in retrospect, questionable decision to manually geotag the remaining 5 years of photos, starting when I bought a point-and-shoot camera in August, 2003.
This took five to ten times longer than I anticipated. I considered giving up several times, but the existence of a definite time bound and the thought "I didn't take that many pictures that year" kept me going. But now I'm done tagging and will soon be able to announce my new (but still too cluttered) gallery. And it'll have pins all over the map!
 And by "manual" I mean "Point Google Earth to the location and then tell GraphicConverter to set EXIF data from Earth."