http://static.yafaray.org/guide/yafaray_course_english.pdf
(ıt is a direct link to the pdf as you see)
It is more general about raytracing , GI (and Yafaray) ...
I found it very informative .
Cheers.
Kadri.
This is a very good article. I read it a while back. It has some useful information on GI in general for any app.