I can't speak to your gyroscope vs. accelerometer question, but the app will always attempt to use the image tracking to resume capturing.
Since the mobile Photosynth app creates panoramas, instead of photosynths, it is important to keep the camera's lens as close to the same place as possible so that the foreground objects lay against the background objects at the same places in all of the input photos. This will give you the best panoramic stitch + will enable the image tracking to succeed on the mobile app.
This is very different from shooting photos to spatially organize with the desktop Photosynth app, where moving all around the subject of the photos in relatively small steps is really the correct way to shoot a synth for 3D reconstruction.
Perhaps one day the mobile app will allow us to shoot photosynths or spin movies ( http://bitly.com/spinmovies ) + moving the camera will not break the visual tracking ( http://bit.ly/gk3dtv ), but not today.