I recently read this in an episode of "Up Close with David": Question:What are the best practices that can help a GTD practitioner maintain a sense of focus throughout a busy day, so that at the end one or two projects have made tangible progress? David Allen:Block a space of time to work on those projects. And doing regular Weekly Reviews will tune up your prioritizing of those things and more motivation to stay focused on them without allowing distractions. So....time blocking can be an integral part of your GTD practice! Cheers!