Our system also provides the question-asker with the option of marking a response "this answered my question" - as with StackExchange. We're currently trying to make this part of our students' routine when getting a question answered...
The system also identifies in which section the question-asker is enrolled, and sends an email notification to the professor for that section. Furthermore, it sends email notifications to the asker whenever their question receives a response. Other students are also able to "subscribe" to a question in order to receive a similar email notification.
We're aiming to release our WordPress plug-in this summer, so I'll try to remember to update this thread with the details once we've put it out in the wild...