Some of my scenes I create, and then a year later I go back and actually RENDER them. Some of the scenes I have created won't be renderable until processors are two or three times faster. Sometimes my scenes go from developement to final render in a day. It all depends on what you're doing! My Hunting Cabin scene, although pretty simple to me now, took over a year to finish. I started it in Bryce 4 on a 64MB RAM machine, and finished it in 5.01 on a 1024MB RAM machine! It still took half an hour to save, but was only 340MB itself... Some scenes just can't be done yet. Try shining a volume-visible spotlight through a simple volumetric sphere. Ridiculous!