What, you think I'm trolling, or somehow implying that closed-source software is better? Oh, teh lulz
I'm just pointing out that, in this specific scene, with these specific drivers, there appears to be a rendering issue. I'm not saying the closed-source drivers are perfect, or ever have been; all graphics card vendors have had major driver issues, and will continue to do so, purely due to the complexity of the drivers themselves, the complexity of the hardware, and the complexity of applications running on top of the drivers. However, the open-source drivers aren't perfect yet. I hope that one day they will be, but at the moment, they're not.
Also, hinting that Nexuiz might possibly have a bug doesn't mean I'm saying it's crap. I'm a programmer by profession, I deal with a lot of bugs in code both I and others have written, day after day.
To prove that I'm not in anyway biased against the drivers, here's a snippet of output from glxinfo on my box, which I ran just now, especially for you:
OpenGL renderer string: Gallium 0.4 on AMD CAYMAN
OpenGL version string: 2.1 Mesa 8.0
See that? Yup, I'm using r600g as I type this.