German hardware site PC Games Hardware has tested SwiftShader from Transgaming Technologies, this new software renderer allows your processor to render games.
As you may expect the CPU isn't really good at this job. The 3DMark scores weren't really high and a Intel Core 2 Quad 3.8GHz (423 x 9) offered only an average of 4.6FPS in Crysis at 800 x 600 with the lowest detail and no FSAA/AF. A GeForce 8500 GT manages to sqeeze 30FPS on your display.
You can check it out over here, they got benchmarks and image quality comparison screenshots. The performance isn't really exciting and the image quality wasn't always that good but it's a pretty cool project.