Also, those who will be in London on November 9 can come to my Code Mesh Keynote. See https://plus.google.com/+CarlHewitt-StandardIoT/posts/BXSZ7Y...
It is fair to say that the implementation of Actors is still in its infancy. There is a startup in Silicon Valley that is attempting to remedy this situation. They are looking for expert programming language and run-time implementers ;-)
Older publications are obsolete and unfortunately many of them have errors (including my own!). I wrote the Wikipedia article on the Actor Model but am no longer allowed to update it :-(
Actors are very well defined up to a unique isomorphism by axioms.
The reason that Actors can perform computations that Turing Machines cannot is that the Turing Machine model left out message passing.
As someone who's been interested in the Actor Model recently, thanks for this statement, and the link to the book you've provided.
This would help avoid going down the wrong path.
Additional information that you might find helpful is here: