Planning a community panel for next year's con—thoughts?

Anyone here ever put together a fan panel for a local convention? A few of us from the forum are thinking about submitting one for next summer's con. We want to do something more interactive than just a Q&A, maybe a game show format or a group discussion on how the industry has changed over the last decade. But we're stuck on what actually works in a hotel conference room with a projector. Do you prefer panels where the audience participates, or ones where you just sit back and listen? Also, how much time should we realistically ask for, and how early do you have to pitch to get a decent slot? Any horror stories or tips from your own experiences would help.