I use it on a daily basis. It's what helps make your drawings and paintings more dynamic and its something that I learned while at art Center.
Pretty much what you should always do, is divide your composition into 1/3's. you do this at the concept, exploration stage. It's kinda like the foundation to the drawing or painting. What this does is create for 4 points of tension where the lines cross. Your goal should be to align the objects in your drawing as close to these points as possible. They're focal points. It creates a more dynamic piece of art as if you would have just centered the object, smack in the middle of the canvas.
Here's an example of a digital painting I did once where I applied the rules of thirds. I did my version of a futuristic Grand Canyon, one that has been colonized n all that stuff. If you notice, I brought out one canyon edge out, about a vertical 1/3. I then placed a little city/dock station on the horizontal 1/3 that crosses it. I did the same thing at the bottom. At the tension points in the bottom is where the Colorado River bends.
Of course its NOT the tell all rule to follow. You can have good composition with out having to follow the rules of third. But it is the backbone of good design. So try it out and let me know what you think!
Using the Rules of 1/3's What it looks like without the guides.