I liked the reference as an introduction to MPI, but it switched between fortran and C so often that I spent a fair amount of my time just trying to interpret the code samples and synchronize to the syntax of the language they were using. You shouldnt have that problem if you have used Fortran in the last ten years but i havnt touched it since college. You have to be able to work with both languages though because many of the key concepts are only demonstrated in one language. Also the examples were usaully spread out into mini snipets as opposed to a larger block that might show a more complete picture.