Mostly it's the people, and only to some degree the technology that impacts the quality of discussions/comments. I.E., 13 year olds on Youtube or XBox vs. working professionals on a site like Quora or Hackernews.
I like how Quora mixes real names and anonymity to try to get the best of both worlds. Google Knol I think supported this, too, but it's a ghost town.
Anon advantages (think Reddit):
* people are more honest, about negative reactions at least
* humor works (doesn't really work on facebook)
* more comfortable to discuss sensitive or embarrassing issues
Real name advantages (think Quora, Google+, some twitterers):
* more constructive dialog
* you can know more about the background of a person contributing - their experience, qualifications, or conflicts of interest
I like how Quora mixes real names and anonymity to try to get the best of both worlds. Google Knol I think supported this, too, but it's a ghost town.
Anon advantages (think Reddit): * people are more honest, about negative reactions at least * humor works (doesn't really work on facebook) * more comfortable to discuss sensitive or embarrassing issues
Real name advantages (think Quora, Google+, some twitterers): * more constructive dialog * you can know more about the background of a person contributing - their experience, qualifications, or conflicts of interest