A simple Greasemonkey script adds one of these missing feature: lyrics. The script creates a container titled "Lyrics" below the video's description and shows the lyrics when you expand the container. Obviously, the video must contain the artist's name and the song's title. If the script doesn't find the lyrics of a song, change the site that provides lyrics (lyrics.astraweb.com seems to be the best) or choose from one the alternative songs.
As usually, to install this script you need Firefox and the Greasemonkey extension.
