This is pretty amazing. I saw the Seadragon/Photosynth demo on a TED video a few years ago (2007) and Microsoft haven't really done anything big with it.
I really wish they would create a version that runs locally, because this would be amazing for architectural work. We are always looking at images in a really linear way, which sometimes takes up a lot of my working time. Having a 3D environment built from site photos would be the best thing since sliced bread.
In the mean time, you can create your own Photosynths on the site, but they are always public.
Below is a pretty good example.
