Some interesting points in this thread, and good suggestions as well.. To this i would add that lighting isnt as simple a thing as many people think, it is a complex artform in itself and not everyone is (or even wants to be) naturally good at it. However the lighting in any scene (no matter which renderer you use) plays a crucial role in the final look. Everything from the positioning, color, brightness etc can make or break the image so you shouldnt ignore it.

So my suggestion is that anyone who feels that their scene is flat or chalky or just uninteresting should get a decent book on lighting techniques. Jeremy Brin's "Digital lighting and rendering " is the industry standard guide on lighting and one of the best books to get on this topic (The guy works at Pixar, what else do you need to know) It is written in a very nice informal manner and never becomes too technical. It isnt specific to any particular software either so you can apply its ideas and settings anywhere. There are also many free tutorials around that cover the basics if you just want a quick look. This is probably a much more sensible thing to try before you dump your current renderer only to find that you get similarly bad results in the next one you pick, because frankly until you know just what is wrong with your image, you wont get better results no matter where you go.