Quote - I am now at 48 hours on this render. Precalculation has finished. It is now rendering. If anything the render process is even slower than the precalculations. The big hold up is the water. I think it is the reflection of the water.

I have a 2.1GHz Core 2 Duo machine with 2GB of memory, so not a high power render machine, but in a "let's see how long this takes" moment I set to rendering a scene with a pool of water (using both reflection and refraction, but with no bump because the water surface already has suitable ripply geometry) taking up about a third of the view. With indirect lighting it took about four and a half days (Friday midnight til Wednesday morning) to precalculate, and then six more days (Wednesday morning til Tuesday morning) to render. Was it worth it? For the render result, no. There are enough small grey splodges that the settings obviously need tweaking. However, I now know roughly how much longer an IDL render is likely to take once it completes its precalculation, so I'll have a better idea when to cut my losses and kill the render.