So many MPI implementations!

Here is an interesting article about "why there are so many MPI implementations" by Jeff Squyres. Some of the prominent MPI implementations are MPICH1, MPICH2, LAM/MPI, Open-MPI, Intel-MPI, MPI/PRO, WMPI, MVAPICH (MPI over Infiniband). List of some other implementations is available at http://www-unix.mcs.anl.gov/mpi/implementations.html. I have some experience in working with MPICH2, where we improved the performance of MPI derived datatypes. My fellow Ph.D. student has a version of MPI called MPI-Mitten to enable process migration in MPI. It seems, everyone wants to optimize MPI implementation for the resources (supercomputer, network interface, memory heirarchy in their machine etc.) available to them based on the need for their application. In my view this is something similar to a recent Cray motto: "adapt the system to the application - not the application to the system". With MPI, it is "adapt MPI implementation for the application".