Totally get you on that. I think that message passing is valuable because it forces you to decouple systems in a way that reduces shared state. But for complex apps this means that you will probably have to introduce some sort of coordination system, which is where things start to get complicated. If you can pull "time" out of the equation (ie look at complete state snapshots rather than messages over time) it can make things a lot easier. Obviously not appropriate for everything, but has worked well for us when building UIs.

No problem btw, fire away if you have any more questions!