Just over a week ago YouTube changed to a new widescreen video format, and today they have official begun streaming HD videos.
Any video that was originally uploaded in HD quality should now be available in HD. To the bottom right of selected videos, simply click the “Watch In HD” link, to load up the high quality HD version.
There is a huge difference in video quality, and it makes the videos a whole lot more enjoyable to watch.
Strictly, the term “HD” should only be used for 720p / 1080i or 1080p resolutions, while the videos shown on YouTube appear to have a resolution of 640 x 360 pixels, or 360p (non full-screen).