YouTube has given a makeover to the individual video pages that reside on their site. The new look is available to those who opt-in to the new design, which you can do here. (If you wish to go back to the old look, just look for the option along the top of the page.)
Here are before and after shots of an individual video page (click an image to view larger graphic):
The biggest change is along the right sidebar, where the related videos section is more fluid and less boxy.
When you do a search in the new design, the video shrinks down but keeps playing, while the results are loaded on the same page:
In other YouTube news, the popular video site is now supporting HTML5. The support is experimental for now. Videos with ads, captions, or annotations are not supported.
You can access HTML5 YouTube by joining the experiment on this page.