As beautiful as this is, it still saddens me that the best we have for efficient cloud effects is drifting camera-facing billboards displaying pre-rendered poofs.
I recently read a paper: Volumetric Clouds and Mega Particles[1]. Here's a demo of it in action: http://www.youtube.com/watch?v=3QqD26SXWDc It looks to be somewhat better than billboards and cheap as well, though it does have some drawbacks.
