During one of the online presentations on the UNconference, one of the speakers talked about how to share Youtube videos without all the ads and comments, which are sometimes inappropriate for some age levels.
Go to Quietube where you can drag the icon to your bookmark / toolbar and then click on this when you want to view the video without all the extras. You can also add the video to your blogs, etc without all the ads and comments.
Lots of other tools shared during the presentation, including one where you can edit a Youtube video so that you just have the section you want to use. It doesn't alter the original. The site for this is called TubeChop.