group called "artsmoke" that has an amazing collection of images dedicated to smoke.
Because smoke is so dynamic, the possibilities are literally infinite. You can never get the same image twice.
The process of capturing images of smoke is very nicely documented in this how-to guide.
There's also this hands-on kind of guide that I found on the artsmoke flickr group, which is also pretty good.
My first attempt at this form of photography looks passable enough.
Next, I need to do this in a room with absolutely no ventilation.