Under Windows
After reading Enko's message, I tried two homes from the gallery. In both cases the program stops after a little thingy spins for a few seconds.

Under Ubuntu
I did some speed tests with example home #7 from the Gallery.
For all pictures: size 1200x900 pixels

YafaRay - Q3 - approx 2-3 minutes
YafaRay - Q4 - approx 13-14 minutes

SH3D Sunflow - Q3 - approx 4 minutes
SH3D Sunflow - Q4 - aborted after 35 minutes

SH3D Sunflow is the original implementation, not one of Enko's plug-ins.
For some reason I forgot to save the rendered images, so I cant offer quality comparisons.

Hans