Quietube is a new tool to enhance the YouTube-watching experience. The idea is that you can watch just the video, with none of the other YouTube page elements. To do this, you simply add its bookmarklet to your browser's bookmarks toolbar, and click it on any YouTube page.
While not as elegant as YouTube Cinema, which is my favorite YouTube enhancer, Quietube doesn't require installing an extension. It also creates a TinyURL you can pass along to others to share the video in Quietube mode.
One thing YouTube watchers may miss, however, is that each video is treated like an embed, meaning that the button for toggling to full-screen view lays hidden within the player's controls.
Here's a quick demo of it below. You can also see a live example of it here.