What's the difference between hardware shading and software shading? Is one more efficient than the other?

Hardware shading requires one of the top of the line graphics cards, and some programming ability, as you have to know how to invoke those hw shaders. And it takes the processing load for the shaders off the CPU and moves it to the GPU, which frees up the processor to deal with other things, like softbody dynamics. 

Thanks.
Yes, I have a good card, the GeForce 6800 Ultra, and hardware shading enabled - I just wondered if it mattered. The CPUs can get quite hot while rendering.

Hello,
for really flexible hardware shading, you need 8xxx or better (shader model 4). Then you can launch CUDA programs on your graphics card. If you look at the latest NVIDIA demos (human head), it's quite impressive. The next generation GPUs (Fermi) will be very interesting, because they can do
double precision arithmetic as well very fast, so wait until next year before upgrading ;-) .

Best regards,
   Michael