I should go watch that debate. From "Elbow Room", the rough idea I've gotten out of it is that traditional Free Will is meaningless and so he invented a new definition which we might now call Agency.
I don't recall how far he took it, but for me determinism is very helpful (if not required) for predictability, and predictability required for meaningful Free Will. So I'll have to go watch the debate, but my bet is that Dennett was willfully (pun intended) refusing to accept the other-definition of Free Will in favor of his own. I'll report back after I listen to the debate :)