My initial observations: Tests performed on: Dual processor 2.0Ghz PowerPC G5 Mac OSX 10.4.8 (current) running with web browser open Processor usage at idle: When Bryce is not the active application, i.e. is not the active window, CPU usage is negligable, in the 1-2% range. When it is the active window, processor usage jumps to 50% per core, or 100% total. I consider this a bug, there's no reason it needs to use a full core if I'm not doing anything in it, regardless if it's the active window or not. It is, however, more even than with bryce 5. Bryce 5 would use 100% of one core and zero of the other, while this uses 50%/50%. I'm not sure if this is due to upgrades to bryce or upgrades to the operating system. If one processor is disabled, bryce hovers around 80% usage of the single core when made to be the active window. Processor usage while rendering: A test scene used 100% of both processing cores and took 0:47 to render With one CPU core disabled, the rendering used 100% of the single core and took 1:23 This equates to a multiprocessor speedup of 76% Interestingly, the rendering process performed one final pass with both cores enabled, and did two partial final passes with only a single core activated. Rendering to disk does not utilize dual processors, and is slower than rendering to screen with a single processor (80-85% usage versus 100% usage while rendering to screen). I also consider this a bug :) Let's see what you've got to share!