I have regularly attended the SQLBits conference in the UK and find it follows a similar pattern to that described however months in advance presenters submit what they would like to present on and the attendees get to vote on which should be included. It certainly appears to work and I always find the session informative and would recommend to anyone. That said it would be great to have some more interactive or discussion sessions too. One of the sessions that does go a little towards this and helps new speakers get a foot in the door is the lightning talks session which is a full session made up of short (no longer than 5 minutes) individual presentations.