I've been meaning to read The Long Tail by Chris Anderson for quite some time. Its one of those books which is endlessly referred to in pretty much every text on the topic of internet sales.
So I settled back to read, and with a heavy heart, quickly realised it was a long essay book. In fact, the long essay already exists, in the form of Anderson's article on Wired.com
The premise of the book is that in our increasingly digital age, the high street point of sale is no longer able to offer the range of goods which the consumer wants. Its a sensible point. I can buy pretty much every song or book ever written, thousands of computer games, and every variety of consumer goods under the sun without leaving my chair. Only a very small range of extremely specialist shops can provide with products which I can't get online, hiking boots are the only thing I can think of off the top of my head.
The upside of this for seller is that, particularly in the case of electronic goods, the shelf space is next to zero, and it only takes a couple of people to buy any obscure MP3 before it becomes profitable. This is also true of 'real' goods, since warehousing is substantially cheaper than shopfront space, Amazon being the obvious case in point.
Unfortunately, I just explained the book. Its got plenty of great examples in there too, in fact, hundreds of case studies adorn its pages, however they don't extend our understanding of the premise.
I was also dissapointed by the lack of discussion about the future of the idea, and how it might be applied. Whilst there is a fascinating amount of detail on Apple, Amazon and others, that's not wildly helpful when it comes to trying to form ideas about how to do something new with the long tail.
So, in the final analysis, I'd recommend going no further than the essay. Its a quicker read, and you'll get everything you need from it.