Chrome extension "YouTube-HTML5-ifier" replaces the flash-based YouTube player with a HTML5 video tag – thus giving you native video playback without the need for a CPU hungry Flash plugin!
The extension can’t show any flash-reliant extras that a video might have, such as annotations, but it does automatically load the best quality video.
Another nice feature thanks to HTML are the auto-fading controls – they only show on mouse over.
Issues
Sometimes videos don’t seem to load so you’re left staring a white box, other times a video will load but won’t play sound until you pause/unpause. Not all videos can be HTML5-ized, either and embedded videos will still play via flash.
Minor quibbles which I’m sure will be addressed in future version of the plugin. All in all it’s a worthwhile extension if you use YouTube a lot.
Download
You can install the extesnion via the Google Chrome Extension gallery @ https://chrome.google.com/extensions