It's my tutorial Jay, but I've based my whole approach to CG lighting on Mr Birn
I'm so grateful to him, because when I first started with Maya I knew this field was the one I was interested in straight away as I'd been drawing and studying light and shadow in the real world for years but I found the technical apects and terminology in Maya very daunting. I think Jeremy Birn must have helped so many people with connecting these two, and I would have struggled like mad if it wouldn't have been for his tutorial and his book so I'm glad Dave pointed me to them when I was new to Maya.
For funny I'm actually reading his book for the second time at the moment as when I first read it I still didn't know mental ray so there were a lot of things I didn't quite grasp. It's called "Digital Lighting and Rendering" and it's a book I'd recommend for people who has a bit of knowledge in this field already to read as it gives you a really good understanding of lighting techniques in production and how to connect CG lighting with elements in the real world, when to cheat and how to do it. I've read many books on mental ray and technical aspects, advanced lighting and materials but this book really stands out because it helps you to understand and improve your rendering techniques so much.
For the hard shadows bullet there's more on it later in my tutorial but the main point with shadows in CG is that they determine the feel in your environments, I'm thinking of doing a shadows only tutorial because you can make so much with shadows in your renders. Look at the real world and you'll see where you get hard and soft ones, but as a general rule hard shadows ocur in harsh and unfrienly environments and where you have artificial light sources such as in a studio where a character is illuminated by spots. Also direct sunlight gives hard shadows. Soft shadows will occur from the sky on a cloudy day and from indirect illumination that bounces, in CG this makes for more comfortable environments where things look more organic.
Get the book Jay if you don't have it, it's more comprehensive than the tutorial and you'll really enjoy it