Have you used Quora? And/or seen who is using Quora? :) They have built what is simply the most addictive Q&A site. It remains to be seen if the usefulness persists once users start coming en masse. However, the potential is definitely there.

Also the team is very well-respected (previously at Facebook) and I think A LOT of people would love to work and learn from them. Maybe even for free for a limited time.