Back in March 2007 Blaise Aguera y Arcas demonstrated SeaDragon (and PhotoSynth) at TED. 3 years later the most common use of SeaDragon’s technology is mapping. The name has changed to DeepZoom, but the basic concept is the same as every other large image handler. I suppose the inspiration for the systems might come from mipmapping.
An impressive demonstration was made by xRez studios, in which they created a number of high resolution panoramic images of the Yosemite Valley. The demonstration can be seen here (requires Silverlight)
The original SeaDragon presentation: