In particular, [Senator Obama] was personally interested in the rise of social networking, Facebook, Youtube, and user-generated content, and casually but persistently grilled us on what we thought the next generation of social media would be and how social networking might affect politics — with no staff present, no prepared materials, no notes. He already knew a fair amount about the topic but was very curious to actually learn more.
An hour and a half with Barack Obama (link from azspot, Marco).
I also highly recommend this article.