Smoke is hard to define graphically. Everyone seems to have a preconcieved notion of what it looks like in a render and alot of times in real life it's a lot denser and chunkier than we imagine. what we think looks good isn't always realistic. It's something that's bugged me for a couple of years - I admit I dunno what to say hear but would care to hear what others have to say so I'll hang back and in the words of Kelsy Gramer's(sp)  Dr. Crane character I'll just say  "I'm listening".

"Speed limit 35 MPH - Fords do your damnedest" - reportedly an old speed limit sign near King's Canyon National Park that was up in the mid 1930s.