Thanks Andreas, that's encouraging info. IMO message-passing makes for a very clean software design.
There is something (probably not for this thread) that has left me puzzled - how to tackle CFD-type problems in the 32KB of memory that is available to each core. From my distant recollections of the Transputer work we did, there was a per-processor overhead of about 128K - mostly "payload" code compiled from Fortran, but also message-passing buffers.
But that's another question for the day that a Parallella board lands in my hands, with a suitably interesting problem to solve!
Mark