FWIW we have faculty using metaFAQ for this purpose (http://www.transversal.com/html/products/metafaq.php). They report excellent results. However, the system is large and complex to run so they are hosted by transversal.
So, we are interested because we have demonstrated utility for a similar use case, but we are concerned about possible complexity.
I'm wondering if there are any plans to somehow develop QA so that it plays nicely with the Polls tool and Samigo/TQ. IT seems like instructors will want to go to one Questions and Answers gateway tool to do all these sorts of things. A question asked in QA might somehow start out as a poll or later enter the TQ question pool after a round of student-student interactions.