I recently made some changes to the cloud script to enable working with particles etc for creating tornadoes etc.
Here is a tornado I did:
And here is a tutorial on how I created it using the cloud generator:
These aren’t smoke, all point density which is better for some things worse for others.
I have other tutorials on this on this thread:
http://blenderartists.org/forum/showthread.php?t=166174
Thought I should create a thread here so new users could find them.