As many longtime Mac users are aware, Flash is one of the most notorious resource hogs available. Many issues have been related to Adobe's media software, causing more headaches than many users feel it's worth. With YouTube and Vimeo offering the HTML5 version for viewing its videos, users can now browse without having to use Flash (videos now play using the H.264 encoding).
Of course, this new technology is still in development and is currently offered as an opt-in beta program on YouTube. The beta does have its limitations for the videos you will see. No advertising (which everyone is disappointed in I'm sure), no full screen options (though expanding the video will play nearly double-sized in your current browser window), no closed captioning, and no annotations.
Users should be aware that the HTML5 standard is only available for compatible browsers--currently Safari and Chrome only. Firefox supports HTML5, but only for the Ogg Theora format (not H.264). Also, embedded videos from YouTube on other Web sites will still be Flash-based.
A bigger implication of popular video sharing sites moving away from Flash is its impact it could have on mobile devices, specifically the iPhone and iPod touch (and perhaps the Tablet). Without Flash as a "missing feature" the iPhone is sure to gain even more inroads to the smart phone market.