Recently there has been stuff that has come up about youtube and possible copyright violation. My position on that is that youtube is diligent at removing content that violates copyright. Therefore, I feel okay posting anything from youtube.
Sometimes there is something that seems like a copyright issue, and later you find out that it was the copyright holder posting it to youtube in an attempt at some sort of weird marketing.
So, I am just stating my official position: feel free to post anything you find on youtube.