Here's the screenshot showing the terrain patches again:
The patches with the same color share the same LOD. The brightness inside of the patches indicates the morphing amount to use, where 0.0 (finest) is represented by a darker shade, while 1.0 (coarsest) is represented by a lighter shade.
Take a look at the patches with the big black X's in them. All the vertices in these patches have a morphing amount of 1.0, which means that their triangle meshes can be replaced by a one-quarter resolution triangle mesh with absolutely no decrease in rendering quality.
Now, when Land-o-Rama detects that all vertices in a patch contain morph amounts equal to 1.0, it replaces the standard index buffer with a smaller index buffer that skips every other vertex in both the x and y directions.
This cuts the number of triangles rendered by 30 to 40 percent, with a corresponding increase in frame rate. w00t!