Modeled and animated with Blender 3D 2.54 Beta. The latest iteration of Blender includes volumetric materials allowing for exceptionally nice looking clouds. Something I've been waiting for for several years now.
This was a test animation to explore the capabilities of the latest Blender builds. I deem this test a success, yet the overall render times are a hindrance to using volumetrics for my more time sensitive projects.
The final result was rendered and composited with Blender's internal renderer on a 2.8ghz dual Quad-Core Mac Pro with 8 Gigs of ram. Each frame rendered in roughly 5 minutes, for a total render time of 72 hours.
Volumetrics are no joke. I'm not sure how much more optimization of the volumetrics is possible but some more work in this area would be nice.