I have 2 GPUs in my computer, GTS 250 and GTS 8800 512 connected to 1 screen each. I want once GPU to drive 1 screen and the other GPU the other one. I have the latest nVidia drivers 310.19 and have enabled Xinerama. The problem is that now unity 3d wont work and neither does gnome shell. If I check the nVidia settings it displays Direct Rendering as Yes. That should mean that I have h/w acceleration but why does neither unity or gnome shell work with 3d acceleration (they run in fallback mode)? Thanks