When you take pictures on the road, you would love to have the latitude and longitude coordinates of each picture stored with it. Indeed, if combined with a digital compass clever software could even tell you what landmark was in the photograph. (ie. if standing on rim of Grand Canyon looking north, it's probably a picture of the canyon.)
To attain this, some digital cameras allow you to plug a GPS into the camera, which is unwieldy to say the least. There's been talk of a bluetooth connection which is better but uses power. On a recent trip Kathryn suggested that the log from the GPS could later be matched up with the timestamps of the photos, which is a great idea -- and a web search reveals a few software packages out there do indeed do this. (And thus also allow photo organizing by geographic location, map-based browsing of photos and other such useful features.)
For the user not wanting to hook up all the devices and use software, I came up with a possible interesting design. Place a memory card slot in the GPS, or allow it to plug in USB or other memory card interfaces. The GPS could then look over the photos on an inserted memory card, read their timestamps, and use its own onboard history of where the GPS was at those exact times, and write coordinates into the files on the flash card. If it can write them on the end of the file that's easiest, if it has to rewrite each entire file that would be a bit slower.
Most digital cameras also have their own USB interface, so the GPS could simply have a USB controller and the camera could be plugged into the GPS after shooting to update the photo files with their location stamps. Most, though perhaps not all digital cameras can act like a USB drive in addition to doing camera control. Of course a standard protocol for updating locations would make this easier, but the main idea allows work with existing digital cameras. (Though they all have their own custom USB plugs and provide their own cable.)
As noted, this can give you great photo organizing. You can see your photos as thumbnails or pushpins in a map. You could link photos to google maps or satellite imagrery of the area. Directories on disk could be created by placename, or even without names photos could be grouped by each major shooting area, instead of just one new directory per 100 photos.
The cameras will eventually get smart enough to be the smart device, but for now the GPS can easily be it. Older GPSs don't have very large track log memories, but today memory is cheap and that's not as much of an issue.