I worked with a CM (at EPCC in Edinburgh, Scotland) in the mid-nineties for a little bit. I think we used CM Fortran -- basically Fortran 77 with extra knobs on for parallelism. I remember it as being a pleasant experience. The programming paradigm effectively hid details of the data decomposition and communications and allowed you to write parallel code in a fairly straightforward fashion. It was also the first supercomputer I go on to, so that was pretty exciting. At the time, the CM was already being eclipsed by the Cray T3D and YMP. Some more ideosyncratic parallel machines I used a bit later were the APE 100 (from Alenia Spazio/Quadrics) and Fermilab's ACPMAPS, which was reminded me of the CM for programming, although I don't know if they were at all similar architecturally.