The new design elements YouTube introduced back in January to 10% of their users are about to be the standard across the site. While they've added a few things, it's mostly all about removing clutter.
The focus is going to be on enhancing the user experience—getting you to watch more than one video per visit in the process. So far it's been successful; YouTube's seen a 6% increase in usage among their 10% guinea pig population.
Some of the changes we already knew about: a strong emphasis on search, and a right-hand column dedicated to video suggestions, and the end of the five-star system in favor of a thumbs up/thumbs down rating. "Liking" a video will add it to a list of videos that you've approved of, automatically generating a playlist of favorites.
What's new: an Autoplay option allows you to play through the suggested video feed, well, automatically. Comments have been reworked, also. There's a separate section for uploader comments, where content providers can engage in a Q&A with the people viewing their videos. Highly rated comments will be elevated to the top, and video responses will be integrated into the flow of conversation.
The changes are as much for content providers as for YouTube watchers; not only is the uploader's name prominently displayed above the video, it can be branded to the creator's liking. The uploader's name and the "Subscribe" button get convenient placing atop the video, and the "More Info" button finds its logical home directly beneath.
So when suddenly YouTube looks a whole lot cleaner, and you can't give a decisive two stars to a Trololo response video, don't say you weren't warned.