Yafaray is an open source rendering engine that is somewhat overshadowed by newer and flasher renderers such as Cycles. Additionally, documentations for it pertaining to Blender 2.5/2.6 are quite hard to find. Most materials are of the old Blender version 2.4x which have a vastly different interface.
However, despite these, Yafaray still packs a punch and can deliver good results within reasonable rendering times.
3D Visualisation with Yafaray for Blender is perhaps one of the few e-books about Yafaray that is pertaining to Blender 2.5 and higher.
Note: The Author is creating this documentation initially for his own usage and out of a difficulty in finding documentation pertaining to newer Blender versions. He cannot guarantee that the material is entirely accurate or even current to the latest version. Under no circumstances shall the Author be liable for damages of any kind arising from the use of this documentation.