Likewise, photosynths are not panoramas, nor are they meant to be.
A photosynth is a way of taking many photos of the same object or scene from many angles and automatically solving for both the structure of the subject matter and the camera positions from the different photos, relative to each other and the subject matter.
In other words, the purpose of a photosynth is to afford you the ability to move between multiple points of view as though you were actually standing on location (rather than viewing a simple slideshow) and secondly, generating a basic 3D model of an object or place which other photos can then be matched against.
The Silverlight photosynth viewer may be choppy, it's true, but the original Direct3D viewer is considerably smoother. You can use it in Internet Explorer (look for the link in the lower left corner of any synth's (not pano's) view page.