Personally, I find that the quality of Youtube comments varies with the content of the video. Some users post videos that always lead to excellent discussion. I think the quality of Youtube comments reflects the quality of the content, more than anything else. Why else would Facebook comments be so bad and sterile? Facebook's content consists mainly of more narcissistic fluff than even a beauty magazine could contain…
So very true. Just last night I spent close to 2 hours reading the YouTube comments on some Romanian "lăutari" music (http://en.wikipedia.org/wiki/L%C4%83utari) videos, and learning so much by doing so. But if you were to move just slightly to watching a related music style, "manele" (http://en.wikipedia.org/wiki/Manele), which are more popular in this day and age, the comments would go way down, at the point where one out of three comments is either racist or a badly spelled swear word.