The appropriate use of lighting is what has the most impact on render times generally, which is why Paolo has put so much effort into training users in the correct use of it.

This is my personal kryptonite with 3Delight AND Reality.  I've been trying reality lights.  So far, I've found them good for very subtle lighting.  Sometimes, I like to blow out my scenes with lighting riiiiiiiiiiiiiiight up to the point where if it got one iota brighter then characters would start washing out.  Like bright daylight beach scenes where there's not a cloud in the sky and not a drop of shade to be found.  I just can't get my scenes that bright with reality/lux and I don't know how to do so.  I nearly got it when I had like 4 mesh screen and the sun light in a scene.. but that would take til 2013 to render in the sizes I like rendering in.