Someone on youtube suggested to make a version of the physics animation from my previous post where the scene is only lit by the small white ball on top. For this purpose I've incorporated the Bullet library to the Simplex Paternitas path tracer of Jacco Bikker. The results are pretty wicked:
This video was rendered on a 8600M GT, 12 spp, 480x360 resolution:
Without caustic noise (only reflective and diffuse balls, 12 spp, 640x480 resolution on 8600M GT):
The new executable and source code are available at http://code.google.com/p/tokap-the-once-known-as-pong/downloads/list
Damn this stuff is really addictive!