Examples of what can go wrong in a classroom when using You Tube without preparation:

On a prac I observed a teacher teaching a lesson using an Australian song. She could not access the version she had used in a previous lesson so opened another one. When the other version of the same YouTube song was opened the year 7 students were greatly amused and the teacher equally horrified when this video included mating kangaroos.

HERE IS ANOTHER EXAMPLE:

If I wanted to use this You Tube.... about indigenous people in Australia....in a classroom I would have problems as some the comments under it include some very racist statements, also on the links on the right hand side are links to other You Tube videos that are not appropriate and also probably attractive to children. Fir example one talks about the coming zombie plague (it is a video from a doomsday church).

http://www.youtube.com/watch?v=dfwy1z5oXHc

So using a safe download program such as iLivid to download ONLY the actual YouTube video is the one save option. 

Blogs are also wonderful places to upload and save YouTube clips. so perhaps the teacher could create a blog just for this purpose and then it could be added here....