If you read the Wired article and/or the blog and was thinking of getting the book, because you're a completist, then don't. There is quite simply nothing new that is in any way important. The corrections to the numbers from the Wired piece have all appeared on the blog. And then of course the irony is strong in this one: This is a book whose only purpose is to sit alongside 10 other "out there" business books in the airport bookshop - as far from the Long Tail as is humanly possible. The potential long tail audience for this book got all the info from the blog already.
It's still a good story. If I have a gripe with the book, apart from the lack of news, it is that I don't think Anderson does much more than point out the technological mechanisms of the long tail. I don't think the outlook on the world that has grown this demand is particularly deep. Reading Andersons book you could get the idea that we have always had this kind of long tail demand and the only news is that technology is now able to satisfy it. I don't buy that for a second.
We live in a society of previously unknown complexity. Complexity creates niches, since nobody can expertly participate in all this complexity. Niches create Long Tail demand. The complexity is constantly going up (because increased complexity adds value), and it's going up faster than the audience is growing, which in turn means that the market is fragmenting more and more. So we should expect demand to skew further down the tail, not because of the structure of the sales channel, but because of the structure of the demand. I think this point is underdeveloped in the book - and I think it is the most interesting aspect of the Long Tail.