Blender 2.70 will have one big new feature: Volumetrics! Not the entire toolbox like point densities or voxel rendering which would be required for smoke. But small things like volumetric absorption!
Some time ago I made a tutorial on how to fake volumetric absorption in Cycles using the ray length-node. The shader was a little over-simplified yet still very complex. The true volumetric absorption coming to Blender 2.70 is way easier to use and gives more accurate results.
In the above image, the left piece uses the fake shader while the middle one uses the new volumetric absorption. You can tell from the bottom part of the piece that the new system is way more natural. One could mimic this behaviour with the old system using a colorramp, but the new system is just way simpler to use. Beware that volumetrics in Blender 2.70 are at a very experimental stage, the interface and behavior are still subject to change. If you want to try it out yourself, here is the .blend. A very recent build of Blender 2.70 is required, though!
You can download the .blend for the above image here!