If I understood the question correctly, how about using 4 recent start-ups that have gained significant traction and have the audience question them on how they did it?
Hum... That's kind of already included because most of the other speakers are succesful entrepreneurs, and they share their stories. But it always sounds easier in hindsight, so I was thinking that by using real testcases of startups that didn't take off yet, you'd understand the challenges better.
Test cases would be very good. I've attended many events myself, Techcrunch50 being the last one and the questions that I ask here have helped me more because I get to ask the same people that have gone through the issue.