Finally, after having thought about the automatic creation of tree models for many months, I implemented my ideas with the help of XNA and HLSL.  The results were absolutely fantastic, far better than I could have imagined:

Yes, admittedly, it's just a trunk.  But it sure is a good-looking trunk!

The trunk is actually just a basic primitive that's being displaced in the vertex shader in real time, which means that the tree model can be changed almost instantly by making changes to the handful of maps that are controlling the vertex shader.  As with terrains, I can generate trees - well, tree trunks, at least - nearly instantly.

The next step is to hammer out branches and leaves.  Considering how well the trunk turned out, I'm confident that the rest of the procedural tree system will turn out nicely!

Long live procedural content.