TKArena has an interesting article about the death of the GPU as we know it:
Have you ever noticed the bases of trees in games today are all hexagons? The number of sides varies depending on the size of the tree, but could involve anywhere from 4-10 sides, then a texture map of bark is stuck on the polygons.
If the tree was made out of voxels it could have been imported from the real world using a laser scanner. The base would be true geometry and every little flake of bark would be real geometry. In a voxel game, each hair of the carpet would be real geometry.
The problem is that computers take time to process each little voxel and so if you make all your characters and your level and every blade of grass and every grain of sand out of voxels, then the computer will take the same amount of time to move a frame as it took the Egyptians to build the pyramids! So at present, the only place voxels are used is in medicine, mining and the sciences.