Thanks for all the input. I agree the use of Boolean as an implicit is definitely not right. Although we can argue about timeout being contextual information, this case is definitely not. It is there merely to express the append as +=. So it is all clear to me to change. Lesson learned.

Talking about context, one other programming model issue I'll have to address is to pass contextual info across actor messages. We have implicits in Scala calls through the stack. We use ThreadLocal extensively for such purposes in a threaded environment. We don't have anything like that in the actor model. Contexts have to be explicitly passed as part of the message. Just food for thought for now. It is best to have these discussions publicly so I'll take it up sometime soon. Thanks again.