Adobe are quick supporting the hardware h.264 acceleration in Flash Gala release http://bit.ly/aixK6s API only publicly documented last week.
On April 22nd, Apple published a tech note on some new H.264 decoding APIs and today Adobe announce that a beta version of Flash Player for OS X – the “Gala” version, calls those hardware APIs for decoding H.264 Flash. (Most “Flash Video” is h.264/MPEG-4 just like the video used for HTML5 and Apple devices, just that Flash is the player.)
That’s really walking the walk on Adobe’s part. Flash on OS X will likely suck less if you have one of the appropriate cards with H.264 hardware decoding on board.