Fair enough, but even the most parallelizable task will still hit the problem of a single bank of main memory (for a multi-core/cpu system) or a single L1 and L2 cache (for HT systems). If rendering were strictly CPU-bound, this wouldn't matter, but it is also a memory-bound operation once the scene hits a certtain level of complexity, at which point you start paying a penalty for not having seperate memory channels. All of this is besides the point, because if it is cheaper to build multiple machines than a single multi-core machine with the equivalent number of cores, and it is easier and less error prone to write code for multiple machines than something optimized for multi-core machines, then as a purely practical matter, multi-core isn't adding value to this specific problem. I'm not saying multi-core isn't valuable...I'm going to build myself a multi-core AMD box here soon, I'm just saying that if all you want to do is spend money on the optimal solution for this specific problem (speeding up render times on hobbyist or pro/am graphics software), your money probably buys you better results invested in more machines.