Pemberton, just to clarify - panoramas aren't Photosynths and Photosynths aren't panoramas. They are both excellent in their own ways, but really are suited to different purposes.
As beautiful as a panorama is and as easy as it is to navigate around it, they have been around for years. ICE makes creating them very easy and photosynth.net provides a great free way to host them as well as a really smooth viewer, but photosynths are actually doing something a bit more interesting and new.
To make a truly great panorama, the lens of your camera really oughtn't move through space, because that would give it a different perspective on foreground objects vs. background objects that would result in panorama stitching errors.
By contrast, to shoot a photosynth, you really need to move all around things so that the computer can track how different parts of the scene relate to each other as the camera moves through, around, or past them.