The new interface shows related videos when you scroll over the bottom of the screen with your cursor. While selected videos on YouTube have had the new design for a while, it's just starting to pop up on videos embedded in blogs.
So now visitors to your website can watch a bunch of videos that you'd never intended to show them without leaving your page. That's, umm.. cool, right?
YouTube's also made it a bit easier to embed videos on your site by adding buttons with the URL and embed code at the end of the video.
[via Google Blogoscoped]