Also, check the Photosynth Photography Guide for keyboard navigation shortcuts:
(Scroll to the last several pages for the keyboard shortcuts.)
In pdf: http://mslabs-777.vo.llnwd.net/e1/documentation/Photosynth Guide v8.pdf
In xps: http://mslabs-777.vo.llnwd.net/e1/documentation/Photosynth Guide v8.xps
Using the free navigation you can easily view the point cloud from angles that you didn't take pictures from.
As for a 'better' viewer, please use Windows xp, Vista, or 7 with Hardware Acceleration set to Full, latest video drivers installed, and DirectX updated. Use Internet Explorer 8 or Firefox 3 and click on 'View Synth in Direct3D Viewer' in the lower left hand corner under any synth.
Use halo/taurus handles in any location where several photos have been taken all pointing inward at the same general point in space to rotate the entire point cloud by clicking and dragging.