Amazing customisation options for Youtube. Removes whatever clutter you don't want from the page. And since it varies what people actually want, it is great that the options are so detailed :-D
I love having recommendations and play-next thumbnails removed. Makes it easier to focus on the videos and I like to think it makes me seem a little cooler when I play a video in a classroom or to show my friends. Every teacher should be using this by the way.