YouTube like anything else has good and bad, and there is give and take. I look at it like this, you can look and see how those Shihan and sensei's you may never get to met, or deciding who to go to, do things. You can also sample before you buy a DVD,or if they don't have DVDs you can see what they do, peers and seniors- for better or worse. You can look at what other people are doing too. It is a way to communicate in a more complete way with others what we do. When things are written down there is lots of limitations to it, but viewing something, it is so much better to see what is being talked about. Without youtube and everything being written down is like a blind date.
Drawbacks are pretty obvious, but I think are outweighed by the positives.