No, I don’t wanna start war ! 
I’ve been working on the toon rendering on my engine,but on a GeForce it works really good, on a g400 not.
Let me explain : I use a 2 pass method (ok, there is a better method using face normals). I draw first the object with 1d texture, then I draw again the object using wireframe, setting the polygon mode to lines, and drawing just the back faces with a line width of 4.
Everything looks good on geForce, while on g400 i can see all the lines, like the backface culling isn’t done.
Here is a snippet :
glDrawElements(…); //textured
glDisable(GL_TEXTURE_1D);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);
glColor3f(0.0f,0.0f,0.0f);
glLineWidth(m_fToonSilTickness);
glDepthFunc(GL_LEQUAL);
glPolygonMode(GL_BACK,GL_LINE);
glCullFace(GL_FRONT);
glDrawElements(…); //wireframe
Thanks.