I meant using the geometry shader.
You can't do it only using pixel/vertex shader.

What i mean is that you can treat data on the gpu however you like, and not be restricted for example to a specific vertex array or index array.

Octree and BSP are meant to cull invisible...

Direct acces to the vram in vertex/pixel/geometry shaders.

This way you can create quite interesting things beside the fact that you could store any kind of information on the card(like an octree...