Flash has been the bane of online websurfers ever since 90s; On Linux and Mac OS X, flash implementation takes up over half available CPU and at high-resolutions stuttering occurs. HTML5 poses answer providing a way for browsers to use native implementations to render videos directly in browser without resorting to ActiveX and 3rd-party browser plugins. Folks at NeoSmart have created an HTML5 YouTube Viewer, just go to here and enter a URL of YouTube video to watch it in embedded HTML5 viewer. You can skip, skim, pause, resume away to your heart's content. Even better, a GreaseMonkey/UserScript let you add a link to all YouTube video pages that points to HTML5 version.
Note: Our testing revealed that Opera 10.x & Firefox 3.5.x doesn’t support streaming MP4 content.