Judging from the feedback from the Stage3D game we sponsored, we don't think the Flash game world is ready for Stage3D hardware acceleration just yet. It seems that 20% of the players so far are unable to use hardware rendering. That's a lot of people!
We could make multiple versions of the game one for software, and one for hardware rendering, disabling certain features etc. but that's not really financially viable as it will increase development time.
However, Stage3D works on mobiles, so it would be a great thing to be able to use the same codebase for mobile versions of our games.
My plan was to use Software mode Stage3D for Flash games, and enable hardware acceleration for the mobile versions. I wanted to replace my existing rendering functions with Stage3D equivalents. I currently use a mixture of draw(); copyPixels(); and bitmap Fills (as well as vector rendering)
So I've been experimenting with Stage3D software rendering.
How disappointing. I'm getting about half the performance of draw() and a third that of copyPixels() from a very simple triangle renderer. So this really isn't viable. Another plan bites the dust!