I'm stealing this text directly from Torsten Hoefler's blog, because I think it's directly relevant to many of this blog's readers:

Our book on "Using Advanced MPI" will appear in about a month - now it's the time to pre-order on Amazon at a reduced price. It is released by the prestigious MIT Press, a must read for parallel computing experts.

He's right.  Go pre-order the book now (I just did!).

And here I'm blatantly stealing the book description from the Amazon page, because it sums up the book better than I could:

This book offers a practical guide to the advanced features of the MPI (Message-Passing Interface) standard library for writing programs for parallel computers. It covers new features added in MPI-3, the latest version of the MPI standard, and updates from MPI-2. Like its companion volume, Using MPI, the book takes an informal, example-driven, tutorial approach. The material in each chapter is organized according to the complexity of the programs used as examples, starting with the simplest example and moving to more complex ones.

Using Advanced MPI covers major changes in MPI-3, including changes to remote memory access and one-sided communication that simplify semantics and enable better performance on modern hardware; new features such as nonblocking and neighborhood collectives for greater scalability on large systems; and minor updates to parallel I/O and dynamic processes. It also covers support for hybrid shared-memory/message-passing programming; MPI_Message, which aids in certain types of multithreaded programming; features that handle very large data; an interface that allows the programmer and the developer to access performance data; and a new binding of MPI to Fortran.

In short: even if you think you're an MPI expert, you'll probably benefit from reading this book.  Or at least having it as a reference.  Or both.

(and just to be clear, I get nothing for promoting this book - all four of the authors are excellent technical writers, and they're all certified experts in MPI; it's going to be a good book)