"Computers are getting smarter all the time. Scientists tell us that soon they will be able to talk to us. And by 'they', I mean 'computers'. I doubt scientists will ever be able to talk to us."
- Dave Barry
This demo shows how to create a procedural fire in a fragment program. The cool thing is that this is achieved in only 8 instructions.
I did something similar in RenderMonkey during my time at ATi. That DX9 HLSL shader was fairly complex though and had many parameters you could tune. In an application you have more flexibility however, so large parts of the calculations can be preprocessed on the CPU. By carefully tuning the parameters passed to the shader I could reduce the number of instruction quite a lot.
Executable