Mac (Snow Leopard): Your Mac's processor can rest a bit easier now. Adobe has release "Gala", a preview release of Flash 10.1 that can utilise graphics hardware to accelerate streaming web videos, reducing the strain on already-hot CPUs.
Hardware acceleration has been exclusive to Windows since the first Flash 10.1 beta arrived, giving Windows-powered desktops, laptops, and media centres a superior experience when viewing YouTube and other streaming sites that use the H.264 video standard. Now Mac users finally get to use their video cards for video.
You can verify that your GPU hardware is being used, according to Adobe, by looking for a tiny white box in the upper-left corner of your Flash videos. The official list of supported hardware is the NVIDIA GeForce 9400M, GeForce 320M, and the GeForce GT 330M.
Test out Flash 10.1 "Gala" on your Mac and tell us about the differences in the comments. It's a free download, and requires an OS updated to 10.6.3. Thanks for the link, SophT!
Flash Player "Gala" Preview Release [Adobe Labs]