Geo-wha? Geotagging. What geotagging is, is a way of attaching information about location to the digital photos that you snap. This will let you organize them and search through them in ways that would not be possible with out that extra info.
Want to create a digital photo album of all the pictures you have from various trips in Europe? If your photos are geotagged you can do this without having to look at each one to figure out where it was taken. The easiest way to do this has got to be Eye-Fi explore. This SD card not only wirelessly uploads photos directly from your camera, but geotags each one as well. For $129 this is not a bad option.
If you want to see more ways to do this? Visit Wired for a GPS add on and using Flickr to geotag after the fact.