As others have suggested, testing potential parrticipants can be a big help. Do the words "grab" in the gut or anywhere else important. Can participants imagine a topic that they would want to put up that is suggested by the theme. The whole invitation that surrounds the theme is critical to a public event. A story about the event, the content, where it might go from the event, etc all set the "theme" words in a context that increases the energy or puts people off. It is what will word in Calgary, and what networks of folks hear about it and trust that it can be their space.
Larry
