I have a Flash 10.1 installer FAIL screenshot as well. It shows the process completed successfully, but it did not seem to need all of the steps to get it done. At least, that is what this progress bar tells me.
With my fingers locked in the save screenshot button combo, I created some Activity Monitor cpu shots while playing the same 720p HD Mortal Kombat Rebirth feature. First one playing it with Flash 10.0 using about 91,7% cpu. Second one, the new Flash 10.1, using about 80,5%. The latest and greatest release of Flash is a little more efficient than last years version. And last but not least, h264 in Youtube’s HTML5 mode, using about 16,3%. So, definitely no hardware acceleration for Flash. But I’m not even sure the h.264 is being accelerated either. I doubt it, because I would expect cpu usages below 5%.