The book Introducing Starling – Building GPU Accelerated Applications, by Thibault Imbert is available for free at O’Reilly. The book description (short version):
Starling is an ActionScript 3 2D framework developed on top of the Stage3D APIs (available on desktop in Flash Player 11 and Adobe AIR 3). Starling is mainly designed for game development, but could be used for many other use cases. Starling makes it possible to write fast GPU accelerated applications without having to touch the low-level Stage3D APIs.
It’s a nice reading if you are planning to dig into the Flash GPU accelerated world.