I love the idea of image metadata, but don't like the idea that if I invest the time in adding it to my photos and Flickr disappears then I've lost it all.
I wrote a Python wrapper for libiptcdata (coming to Debian if the NEW queue ever moves) and some tools to add titles, keywords and comments to IPTC data (embedded in the JPEG), which fixes one part of my problem.
Although one day I might have a camera that has a built-in GPS, until that day the next best thing is Google Maps. Since they added Australian street data, I can pretty much pin-point wherever I was in a matter of seconds with a place name search. Using their API I hacked up a latitude and longitude finder page which can search by address, and pops up information in a format suitable for pasting directly to the exiv2 command line to embed the location in the EXIF data. You can also click anywhere to add a mark and then click on it to get its location information.
The only problem was that EXIF expects locations with degrees, minutes and seconds rather than the more modern decimal points, which makes ye feel a bit like a scurvy old sea dog, ahhrrr.
Flickr can also apparently take geographic information from tags, if you paste them in and know the secret page to import it. However, when uploading with EXIF GPS data I found that it placed things on the map straight away and doesn't pollute your existing tags. Yahoo maps are however, at this point, unfortunately a fairly mediocre imitation of Google maps.
Yay Web 2.0!