Photographing smoke can often be a tricky endeavor as it can throw up all sorts of weird exposure problems. On the upside, however, it can really be used nicely to enhance the composition of a photograph.
These photos all use smoke in some way to enhance the composition of the image. Whether it is to provide a sense of movement, to guide the eye with lines or to provide a atmospheric layering effect, they all effectively use smoke to create a more interesting photo.
Photo by Eggman