Today, YouTube revamped its video editing page to make it easier to edit YouTube videos.
As first spotted by the unofficial Google Operating System Blog, YouTube today sports a whole new Cloud video editing interface.
YouTube had previously tried a Flash-based editing system a few years ago called 'Remixer' which wasn't very reliable and therefore unpopular.
'Editor' isn't based in Flash (though the output will be played in Flash if you don't have HTML5 video enabled) and therefore doesn't have the processor and memory overhead that is common in Flash web applications.