>Btw if you mention Purcells Paper it is
>only fair to mention Carr et als, too they have a paper at the
>same conference with the same topic (GI strategies) on GPUs.

A minor correction:

Nathan A. Carr, Jesse D. Hall and John C. Hart. The Ray Engine. Proc.
Graphics Hardware 2002, Sep. 2002 (can be found at
http://graphics.cs.uiuc.edu/~jch/papers/)

was at Proc. Graphics Hardware, not SIGGRAPH 2002 (where Purcell's paper
was presented). The thing I like about Purcell et al. was that they put
just about everything they could on the GPU-side; Carr's approach is more
limited.

They also have another paper of interest this year (I haven't looked at it
yet):

Nathan A. Carr, Jesse D. Hall and John C. Hart. GPU Algorithms for
Radiosity and Subsurface Scattering. Proc. Graphics Hardware, July 2003

Purcell's been thinking along somewhat similar lines, see
http://graphics.stanford.edu/papers/photongfx/.

Eric