Once you started running around in it at first I thought you might have used Marching Cubes or Marching Tetrahedrons, but you are just placing the vertices of a plane that is usually done with a height map it looks like.

Still cool. I love this stuff. I mess with weird side projects like this all of the time too. I blogged about some of my voxel, tile, and other side diversions today.

Looks cool. Are you just using a Vertex Shader there?