I've been following how Tony Hsieh of Zappos and other companies structure their business models. This is a great audio book that can be downloaded for free that describes how companies at different stages function.

If you are an entrepreneur and love learning about business, this is a must listen/read. I plan to get the Kindle version after listening to the audio.

http://www.zappos.com/tribal.zhtml

It means you better be quick and nimble, or Jack be dead...