Everybody links to it, and it is by no means the first book to be done in this way. Not at all the first book. But still: The blog on The Long Tail - the book that will follow the landmark Wired article on the network economics that gives online retailers their edge - is fascinating.
Among the fascinating things: The numbers in the articly on the percentage size of the tail is no longer third party research, but instead numbers from Amazon. Obviously it is a lot simpler to extract that kind of answers when the book writing process is public (there's good marketing in giving the numbers). And obviously the kind of Beer Review* that you get in the blogspace is also valuable.

* Beer Review: The blogspace analogy of the Peer Review of the academic world. I think the term is appropriate also to describe (by way of a pun) the average quality of opinions uttered in blogspace. Some are great. Some just drunken nonsense.

Since this term obviously makes sense in and of itself, it's impossible for me to assert that this particular pun has never been used before, but I certainly haven't heard it before.