The most interesting thing about Photosynth is the possibility to have your images mapped in 3d space. A "classic" panorama is shot from the NPP (no parallax point) so there is no depth information available.
This changes if you're capturing stereo panoramas. They contain the needed depth information, just like the human stereoscopic view with 2 eyes.
I uploaded 2 stereo panoramas from the flak tower in Vienna to Photosynth to see if it really works ... and it did:
DirectX viewer !
Here is a link to the default Silverlight viewer, along with the second panorama. The most impressive views are the overhead view and the point clound zoomed out:
Along with the stereo panorama tests i also tried to capture a scenery for 3D by simply capturing a video while walking around. This video acts as an image source for the synth:
The result surpasses my expectations: