I remember being the attendee at the first CBO Days back in 2006. Mohamed Zait was at time already involved in the developing of the CBO and had several excellent presentations. It was a great opportunity to discuss with him the actual problems we had with the CBO at that time like the bind variables peeking only at the parse time and run-away queries. At the OakTable dinner we suggested him several possible solutions which were in subsequent years built in the database.
Such kind of events are great opportunity to get the knowledge which one can't really get at one place. Internet is a great source of knowledge, but attending a detailed technical presentation is something quite different.
I expect that this event will be simply the best event totally focused on the problems of the cost based optimization.