I'm lovin' this article: http://www.defmacro.org/ramblings/concurrency.html.
It meshes nicely with my earlier post here. Erlang is like stackless Python with coroutines in that it's a lightweight threading system built on top of asynchronous IO. However, it's different in that there is no data shared between threads (i.e. a shared heap protected by locks). Instead, to share data, you must use message passing. This part matches my earlier post. Of course, the benefit is that it's trivial to do distributed computing with such systems.
Anyway, Erlang has been around a long time and is incredibly robust. I'd love to get a chance to use it.