I remember back when I needed more than one hand to count render time in minutes. Now if an HD frame takes more than 2 minutes I get antsy.
How do I keep render times short? 1) Use an absolute minimum amount of ray tracing. I cache ambient occlusion in point clouds for non-deforming objects (and also for many deforming objects – it really doesn’t look bad). 2) Stream all input to the renderer in a single pass. No writing RIB or other big intermediate files to disk.