Suppose you have a lot of photos all with the same object in them, or photos from the same area. Navigating the photos as thumbnails doesn't work very well when you have more than a handful of photos.
A Univ of Washington team has a demonstration of a system for navigating the photos in 3D. The system computes the relationship between the camera position among all the photos, then allows you to "zoom in" on the object by finding another photo that is closer. Or it allows you to "circle around" an object by finding photos to the left and right.
This system does not attempt to stitch photos into seamless panorama, nor does it attempt to build a complete virtual 3D world. But the effect is almost that good.
They've produced a 5 minute video demonstrating their system (Flash). Scroll down on the page for a description of the system. You You can also get all the details on the team's main project page. Microsoft Research has some beta software based on the UW research (I haven't tried it out yet).