I would ask anything where there isn't a clear cut answer and which usually involves strong or varied opinions and/or emotions from human participants. For example:

• What do do you think of the current situation in Libya?
• What are your thoughts on the recent disaster in Japan?
• How do you think we should resolve the humanitarian crisis in the Ivory Coast?
• Why do you think Coldplay became so popular?
• What do you think about Charlie Sheen?
• What new technologies should we foresee in the next twenty years?