Though YouTube came with a solution of using an iframe code which can handle display of video in non flash supported videos, youtube-html5-chrome, an extension of Chrome browser has taken a step in same direction.
It replaces the standard Flash-based YouTube video player with HTML5’s new video tag which natively supports video. Video played this way will be more efficient and require less CPU. An attempt is made to automatically play the best format possible (HD if available).
Though there are still issues with this extension but the way people and developers are responding, You might love to keep an eye on it for upcoming versions.