Sand - 6:26 pm on Aug 23, 2012 (gmt 0)
If you have a question and answer site and you want it to do well in Google, then the best thing to do is moderate the hell out of it to ensure quality. See Stack Overflow for a good example of how to do it right.
As for questions with no answers: think about it from a searcher's perspective. If I'm trying to solve a problem, I want an answer, not confirmation that someone else at one point had the same question I do.