Brynjolfsson is one of the most forward and provocative thinkers out there about technology and its impact on economics. The book he co-authored with Andy McAfee "Race Against the Machine" is one of the best books I have read in a long time. This book repeats much of what is in Race against the Machine, giving it a more positive spin. If you have read the first book, there really is no reason to read this one. The Second Machine Age rewords much of Brynjolfsson's TED talk of the a similar name. The TED Talk is highly recommended and provides a good overview of what you will find in this book.
Big ideas, like those Brynjolfsson talks about are hard to come by and that is what makes them valuable. I had hoped that this book developed these ideas further, rather than largely restating them. That said if you have never read "Race" this book is just as good as the other.