Today I've read news about Adobe Flash 11.4 and get an idea to test how Pepper Flash plugin works on Linux.
Last time I tested 11.2 release and it's was completely unusual, because hardware acceleration was disabled by Adobe.
Here is topic about that on phoronix: No OpenGL for Flash Stage3D on Linux.

But today I checked latest version of Google Chrome and find that situation is completely changed.
From Stage3D now disabled in plugin, but only disabled in Google Chrome configuration by default.

There is screenshot of Unreal Engine 3 flash demo:
1920x1200 screenshot
My configuration is: Ubuntu 12.04 32-bit, AMD HD6950 1GB, FGLRX driver, Google Chrome 21.0.1180.81 with flash player

Try this:
  1. Install latest Google Chrome
  2. Run it with "--ignore-gpu-blacklist" flag
  3. Open chrome://gpu-internals/ and check Stage3D status
  4. Serf to or any other demo

PS: For me it's even works on notebook with mobile Intel i3 and HD3000.
Performance is quite low, looks like 10-15FPS, but all textures is here and all effects working like on HD6950.