I’ve written a simple particle system that abandons the use of display objects. A typical particle system in Flash would often use Sprites or MovieClips that have their properties updated by a single enter frame. This can usually result in performance issues if they are not removed properly afterwards. The particles in this example are drawn to a sprite (off stage) every frame, then the container is drawn to a bitmap. I’ve had about 5000 particles being drawn each frame, effortlessly.

Flash 10 Circles