A photosynth is a collection of photos taken at many *different locations*, all looking at at least one subject (possibly more than one).
Since the photos are all taken at different perspectives, there is no way to merge the photos into a single chunk of photography without distorting them, so they are kept separate. What taking photos from many different points of view allows, however, is for Photosynth to start reconstructing a rough 3D model of the subject of the photography. This is something that no panorama does.
For example, if you view this link http://bit.ly/orbitalsynth on a Mac or a Windows computer, you'll see my photosynth 'Orbital Propulsion (Gravity Assist)'.
If you're using a Windows computer that has the Photosynth app for Windows installed on it, you can use this link in Internet Explorer: http://bit.ly/orbitalsynthd3d
If you want to see it on an iPhone, you'll need iSynth ( http://bit.ly/isynth ) and search for 'Orbital' and you'll find it.