I agree with the above, the smoke looks a little square in parts instead of free flowing like smoke should be. That being said, i quite like the effect you have done with it. I would have like to see this effect added to a picture to give it a little more depth. As a background though, I think it is very effective. Good effort.
The blue and dark colors in their swirl is quite pleasant to the eye.
All I can say for improvement is that bright white, unwispy piece in the center. It contrasts the rest of the colors almost too much, and is a bit geometric. So I agree with Andy. Overall looks good, just that one little thing in the middle. Hope that helps.
thunder rolls across the sky
as black rain pours down into the night.
the essence of sorrow, like tears being shed;
like drops of pain upon my head.
blindly walking with no sight-
always darkness, never light.