Smooth Normals

Yes sir, if you ever wanted to torture a GPU, right here's the best way.  Path tracing with no acceleration structures, using two 128-bit textures to store scene data, 100+ triangle intersection tests each step with barycentric normal interpolation, and, as if that wasn't bad enough, a heterogeneous participating medium.

Kudos to you, EVGA GTX 560, for surviving the bloodbath.

Yes indeed, that sphere in the middle is made out of triangles.  I'm not too sure what's going on at the edges...can't tell if those are just artifacts from it being a triangle mesh, or if there's actually a problem with normal interpolation.  For the most part, however, it looks good.