Michael and Mark from the Scout team just published an awesome article on the internals of Flash Player and how it relates to Scout. I am sure you guys will love it. The article is available here on Devnet.
The article starts with an overview, then dives into details like how Flash Player instances work, the core components, ActionScript 3 event handling and how "core loop", the beating heart of the Flash Player works.
It does not stop there and also covers topics like rendering side and how the display list works but also the network stack and more. The article ends with general GPU related performance issues. A must read for every ActionScript 3 developer.