Piper's new book on the New Perspective on Paul (NPP) is now available, online for free, if you like reading books on your computer. You can also order it if you like.
If you are not familiar with the NPP, this book will likely be of little interest to you. In fact, it might be more confusing than helpful. (I haven't read it, but am surmising this from what I do know (not very much) and from what the Desiring God blog says.)
Surprisingly (to me), Doug Moo has at least some sympathy for Wright and Dunn (two major proponents of NPP). He says that NPP has some legitimate insights by reading Romans in light of the first century rather than the sixteenth century. It is, in Moo's view, similar to Webber's Ancient Future Faith, which has been fairly influential particularly in some emerging circles. The idea of Webber was that we can better understand the church through a better understanding of the early centuries of the church, particularly through understanding the church fathers. Therefore, by understanding Paul's context (first century Judaism) rather than Luther's context (16th century Romanism), we can have a better understanding of what Paul was actually addressing.
Moo does stop short of endorsing their full conclusion (whatever exactly it is since it varies from person to person), though he holds that there is some sense of future justification and rejects the neat "in the box" explanations of the warning passages. He nuances it fairly carefully, and humbly, IMO. Moo notes that many of the opponents of NPP been more polemic than accurate in their evaluations and refutations. My understanding of NPP is that there are some serious problems, particularly in the area of justification.
Anyway, all that to say that Piper's book is now available.