The viewer sometimes stops responding to mouse motion for no
apparent reason, although I think it is related to a zero
sized 3D scene. Keystrokes continue to work.

There are mismatches in reference counting between Performer
and Python.

    A) Sometimes the Python gc counts get out of sync and are
    reported as an error. Reloading the scene with 'L' usually
    fixes it.

    B) Animation engines generate lots of mismatches and often
    crash the viewer or leave junk in the scene when reloaded.

When viewing an entire directory, changes often result in
the main.py3d being re-executed twice. Sometimes changes to
imported modules don't get picked up.

Using Performer multiprocessing on hyperthreaded x86 systems
sometimes locks up when you try to exit, for no reason that
I can discover. Since it's unlikely that SGI will ever fix
this bug, multiprocessing is now off by default on Linux.
You can turn it on with -mp