If you want a HN example, take my post on "Google's Android faces a serious Linux copyright issue."
http://news.ycombinator.com/item?id=2337340
It was moderated 8, and contains the precise answer to the issue/controversy (it quotes the exception from Linux's COPYING file that both LWN and Linus himself cited later to refute the alleged "copyright issue")
The highest-voted comment on the article (38) does not mention this exception, and is full of inaccuracies like "Unless these programs are actually copying parts of the kernel into their source, they are not derived works."
Show me a reason to care. All I know is that expertsexchange needs to die in a fire. I don't care who pushes them into the bonfire. :D
This post, about John Nash, validates my case.
I use StackOverflow for work. Real work. The thing where you get paid.
Quora only entertains me.
In my view, it's some sort of wikipedia Q&A. I don't value it really highly.
The site itself has some impressive features but also some bewildering layout issues. One problem is - how much bigger can the site get before the quality of the participants is diluted too much?
Taking what other posters saying are saying a little bit farther: stack overflow is for work, quora is for fun, metafilter is for nothing.