Good point. I forgot about 0MQ. Yeah not everyone will learn a new language but still want to build a distributed system. 0MQ is great for that.
With Erlang, which was perhaps confusing from my post, the Pid identifies an "Erlang process". It is a very light weight unit of execution. One can have tens of thousands of them in a single OS process (which they call a node).
However, if you don't need tens of thousands of processes, there is not reason why one couldn't structure their app using real OS processes and using 0QM.
For anybody interested in the topic, I would also recommend to read Joe Armstrong's PhD thesis:
http://www.sics.se/~joe/thesis/armstrong_thesis_2003.pdf
It is a well written text on building reliable distributed systems in general, and Erlang in particular.
That's why I started learning more about ZeroMQ http://www.zeromq.org and structured my latest work project as multiple processes instead of multiple threads. Each process is single-threaded, and (at least so far) relatively easy to reason about.