I'm using the Windows 8.1 Preview and on Youtube videos still flicker and the graphics driver still crashes. And I even downloaded the same drivers from the NVidia website. I found them in the Windows 8.1 thread in the NVidia forums. No difference! I have the Asus Geforce GTX560ti top series.
I have the 560 too, you might want to try what I did and downgrade to 310.70 and uncheck "check for updates". I don't get the Youtube flicker issue you do, for me the card overheats in normal desktop mode It's a known issue with older cards (and some newer) since the 320.x versions if I recall.
Guess I won't upgrade, and not fix what ain't broke Thanks guys