We just pushed a few minutes ago a new version of the Flash Player 10.1.82.76 containing a nice feature that was in beta until now called "Gala". Yes, H.264 GPU decoding in Mac OSX is now officially enabled in the Flash Player.
You should notice now a nice difference when playing H.264 content on your Mac in terms of CPU usage. We rarely enable new features in security releases but we really wanted to enable such a cool feature. For more details about it, Tinic already posted about this.
Of course, you will not see the tiny top left white rectangle anymore, we removed it.
Noe that we are actively working on improving even more the video experience in the Flash Player, more about this soon.
To download the latest version, you know where to get it
It may take a few hours to get propagated, so make sure you double check the version.