Here is a demo that shows a particle system entirely on the GPU in OpenGL. This demo requires a shader model 4 compliant graphics card.
More info and download HERE.
Naixela released two demos “geometry shader painterly rendering” and “geometry shader tessellation” taking advantage of Shader Model 4 (inclusive source code).
– Geometry Shader Painterly Rendering Demo
Renders a scene into color, position, and normal textures, and then outputs the scene as a large number of brush strokes covering the screen using the geometry shader.
– Geometry Shader Tessellation Demo
Tessellates a heightfield based on distance to the viewer using the geometry shader.