An interesting side effect to the whole capture/review cycle is that if you do it effectively, you will discover that the goal of "getting out of your head" is a red herring. It's not so much "get it out of your head"; rather, it's move it from the "holy cow, I gotta do it now!" spot in your brain to the "yeah, it's cool, I know its written down so I don't have to panic about it" spot.
Interesting point! I like the idea of different parts of the mind vs. it's completely out of the mind. The items are just in the more relaxed part of the mind (ideally).