“I just saw the amazing film UP! and the beautiful short film Partly Cloudy and almost burst into tears when I first saw the cloud characters of the second one (Fig.01 above). They were simply awesome! The render was just so nicely accomplished that I couldn’t believe my eyes for almost half a minute ‘ so when I finally did, I thought to myself “I should figure out a way to at least render in Photoshop clouds like those!”
http://www.3dtotal.com/team/Tutorials_3/rendering_clouds/clouds_01.php