Athlon II X4 640
8GB Ram (DDR3 1600)
AMD 6790 1GB
1920x1080 panel
Running on Fedora 16 with Catalyst 12.2
I go from 60 fps (vsync) to 30 fps with the deferred shadow enabled in many areas. I will have to try it on my Windows box with an Nvidia GTX460, as it could be an AMD card in Linux issue.
Here are two screenshots, one with, and without the celshading active. The drop is at least 20fps in these shots.
http://evan.action-web.ca/misc/darkplaces/celshaded.jpg
http://evan.action-web.ca/misc/darkplac ... shaded.jpg
Also, for the effect to work, you need new textures. I replaced the detailed textures on some of my weapon models with flat textures, and the effect is much better in those cases.