Actors in Clojure -- Why not?

The article seems largely theoretical in nature - "efficient Actor implementations are possible". Why no links to these implementations? And if they actually do exist how do they compare to Clojure's use-it-today high performance single-machine concurrency implementation?

Also, his counterpoints sound like they either add incidental complexity or refer to papers not implementations.

In anycase, Rich wasn't banging on Actors. He simply was arguing for his approach to concurrency over one of the most popular Actor implementations actively used in production today - Erlang.

And finally, here's a pretty interesting project for distributed computing with Clojure: http://github.com/amitrathore/swarmiji

Clojure's mechanisms for concurrent state are more powerful and flexible than actors. Clojure's agents actually have a lot in common with actors, but take arbitrary functions instead of predefined messages. From a Clojure point of view, actors are agents with restricted functionality to enable use in a distributed environment.

Adding actors to Clojure might be a good idea, but they should be explicitly for the purpose of distributed systems, and probably built on top of agents.