Nice article.
About using test doubles for entities, I think it also depends on how rich your model is. If your entities have almost no business rules, then there is no point in using test doubles. It's cheap to use the actual entity in your test, and you don't have to assert method calls anyway.
But if your Entity is taking care of business rules, you most likely will call entity methods from your service. In this case, I find usefull to mock entities so I know that those method calls (I mean commands, not queries) are being sent correctly. I think it's easier to use interaction based testing, since you don't always have the possibility to assert the entity state using state based testing: you don't always have a public interface for that.
I'd love to see your thoughts on this.