version 0.0.2 is now available and gives you the same possibilities as vertex colors instead of vertex weights. If you have installed the script you can find this new functionality under Paint->Height.
Terrain modellingThe script was created with terrain modelling in mind. You might for example want to distribute plants based on the height of a landscape mesh as shown in the (rather crude I admit) image below:
The image was created with a mesh from the ANT landscape generator to which a vertex group was added with the height addon (in weight paint mode, in the 3dview with Weights->Height). The result was this weight map:
Because i wanted the grass particles to be more dense at lower altitudes, I tweaked the weights in the resulting vertex group with a vertex weight edit modifier with the following settings:
The resulting map (shown below) was then used a density map for my particle system: