In preparation for the release of Harry Potter and the Deathly Hallows, I've been rereading the first six books. When I got to Goblet of Fire, I realized that Dumbledore has found his own system for GTD. He clearly knows the critical concept - empty your mind of all the open loops and put them into a trusted system. With your mind clear, you can use your trusted system to evaluate the work you need to do and define the next actions.
Dumbledore's system? The pensieve. Remember when Harry enters Dumbledore's office to tell him about Barty Crouch (Sr)? He falls into the pensieve and witnesses Dumbledore's memories of the Death Eater trials. When Harry emerges from the pensieve, Dumbledore tells him that sometimes he has too many thoughts in his head. It helps to pull them out and put them into the pensieve to observe.
I now must check the David Allen Co. store to see if he is selling pensieves yet.