It's a tool that is only as good as the people who use it. I've relied on it while teaching, since there are many unknown gems out there.
That being said, I've never seen anything stupider then some of the comments left on certain videos. It is like they took the worst kind of people, lowered their IQ a few notches, and let them loose in the video comment sections.
EDIT: Here is an example...I once even received some PM from a metalhead who tried to convince me that Hitler managed to take over based solely on his restriction of civilian gun ownership. When I reasonably pointed out that while he might have used gun restriction as one of several means to maintain power, he came to power by exploiting a longstanding tradition of antisemitism in Germany (and elsewhere) he then PMed back a long-winded and incomprehensible rant about how I was a "sheeple" and that I needed to "wake up".
This is the quality of person you deal with there, it seems.