Dear Kninjanin,
Yes, for me communication is definitely better, and higher quality also, than social networks. But if the site owners are not very very careful, then all the problems Rooster mentions can really bring a Q/A site down.
At one time, I was quite fascinated and delighted about the potential for Q/A sites to bring about international communication, as well as learning, among the people of the world. However I have lost much of that optimism as I watch a few good sites go down when the owners find ways to make more money! So I think a good Q/A site would almost need to be run by a non-profit organization, with the goal of fostering communication and learning among users.
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Also, I have learned that good moderation is very difficult. Most people do not have enough human understanding to moderate well. Rooster is an excellent moderator and he could teach others how to do it, but he did not really have enough say in how that site was run so it turned out extremely difficult for him.
But yes, I definitely agree with you that communication is SO much better on Q/A sites than social networks!