Allowing the delegates to largely set the agenda for conferences and conventions is a common trend these days. Going well beyond a Feedback form distributed at the previous years conclusion, there are ways to really involve the delegates into content, topics, speakers and activities.
Interactive websites and discussion boards can easily be used to collect ideas on Topics and Areas of Interest.
Delegates who then register early for the event are then enabled to influence the final choice of agenda.
Not only does this give more ownership of the content but also is an incentive to book early.
A search of UnConference, Open Space and BarCamps will reveal many approaches to this.
Here are a few links to get you started
http://money.cnn.com/2006/06/05/technology/business2_unconference0606/index.htm
http://en.wikipedia.org/wiki/Unconference
http://www.unconference.net/
