I guess the title is keeping with the theme of Halloween this week. :)
Shadows play a large role in renderings as they help to set the mood of a scene. Whether something is scary, daytime, nighttime and more is controlled not just by how much lighting is in your scene but also where your shadows fall. I have been reading a really good book by Jeremy Birn that explains the techniques of lighting and rendering in a way that is not specific to any piece of software.
One person (whose site I recently ran across) that makes good use of shadows and lighting is Rudy. The environment scenes he produces look quite good (especially Gallery 04).
In your next rendering project spend a bit of time examing different lighting options. If you use one key light add a second fill light to help add a small bit of environment light to you scene. These little details make all the difference.
For those of you looking for the Architectural Illustrative Rendering tutorial with photoshop, this will be posted over weekend as I put the final touches on it.
Happy Rendering...