Youtube is a great place to watch videos. But, the web interface can be quite distracting with comments, advertisements and related videos. If you don't like this, you might like to watch Youtube videos in a native application.
Minitube is a great little Youtube viewer application for Ubuntu. Just search for the video you want and it starts playing. The pane on the left shows the search result videos. There is also an option below the video to switch to higher or lower quality video streams.
Minitube is available on the Ubuntu repositories, but this old version does not work. To get the latest working version, add the PPA repository ppa:nilarimogard/webupd8. Update and install Minitube by using the package name minitube.
Tried with: Minitube 2.0 and Ubuntu 12.04 LTS