I don't mind continuous redesigns or small tweaks. I like it when products and apps I use subtly but constantly change. Form and function are one, it's not form over function if it's done well.

But for YouTube I wish they realized that the majority of the design visitors experience is in the user created content. And they should start policing it. A good first step would be to stop having user selected thumbnails. Video titles should be under the thumbnail, not word-art added on by the creator. Then the video thumbnail itself should be just be a calm still image representation of the video. A video having a thumbnail with a person having an extreme facial expression overlaid with enormous neon text should just be throttled to get 0 views by hiding it from view.