In his book programming erlang Joe Armstrong talks about how erlang is OOP in the original sense. You spawn a bunch of light weight processes, and each process is like a living function with its own brain. Pony is a new similar language. Each process can only communicate with the outside world through message passing. You can easily define the semantics of sync vs async, and what to do if something fails. If something does fail, you've decoupled the error handling, and you can respawn processes, even if it was caused by a flipped bit of ram. If you're just synchronous message passing, then it should be just as reliable as java/ruby, and not much slower.

There's still some down sides in that now you can easily get race conditions on human error, you're dealing with distributed systems problems. You have to worry about defining your communication interfaces and keeping them updated, and resilient to change. Message passing has a lot of trade offs.