I think most of us have used youtube at least once, I know my first experience was when a friend emailed me a video she thought was funny. I just recently started to look up things I could use in my teaching, mainly I used it as a resource to get new ideas or see what others were doing.
Every year at my school we have difficulty getting all our sixth graders to be able to open their lockers, its a new experience for them and many have never opened a locker. And one day I searched on yourtube 'how to open PE locker,' and found there were numerous videos on the subject. What I'm going to do next year is pull the video off of youtube, a friend told me of some software, and show it too all the sixth graders.
I think youtube is a great resource, but you have to be careful, when I looked at the posts below I saw several that were inappropriate for students to read. I've also looked up how to take care of injuries, like how to treat plantar faciitis.