There is no need to download a plugin to watch HTML5 embedded video. You can customize the player. You can customize the content.
But what about Flash? With HTML5 you can watch high definition streaming video without the need to download the Flash plugin or use javascript.
What about IE? There's a workaround for that too.
Right now all but one major browser vendor supports HTML5 video.
Mozilla Firefox, Mozilla Camino, Apple Safari, Google Chrome and Konquorer all support HTML5 video.
Internet Explorer does NOT support HTML5 video tags. You can still embed an MP4 or Flash file to play the video as a work around without too much hassle.
Don't expect Flash Video to go anywhere soon. With it's limitless interactive possibilities Flash will continue to be a major player on portable devices as well as desktop platforms for years to come.
Should you abandon Flash video? Not just yet. As with all emerging technologies it's better to wait and see where this goes instead of jumping the gun.
It's never too early to start using new technologies as long as you have a fool proof fall back system for older browsers.
It seems right now the only way to fall back for older browsers that don't support HTML5 Video tags would be to use Quicktime or Flash Video.
This, of course, depends on the users browser plugins.