Here’s a workflow to save time that works pretty well for some scenes. The first video below is a pencil modeled, textured, animated and rendered with Blender 2.66 (cycles). Each frame takes my machine from 4 to 12 minutes to render. It has 250 frames + the first frame and last frames are held for a few seconds.
A shortcut to get a lot more frames (nearly twice as many here) is to use slowmovideo from granjow. It’s now available for both Windows and Linux, and this vid only took about 30 minutes to render:
If you already have a sequence of frames rendered out and want to change playback speed for dramatic effect, it has an advantage on the VSE because it can interpolate between already rendered frames:
This algorithm gets strained for some kinds of scenes (for example it really choked on one of my scenes with train tracks), but using it on the second video above literally saved 20 hours of render time to create.