What goes around comes around and one of my hobby-horses has come around again. My personal approach to GTD coaching is to emphasis the mental game. It is not about having a particular set of macro's or a specific tool. It is about how you think. For me this is very basic, but I keep having to prise people away from a technology of some kind and demand they do their own thinking.
It is a great human weakness to wish for a magic wand, the device, glistening and replete with hard-coded wisdom, that will fix your wagon for good. It should dovetail itself to your psyche without actually needing any kind of conversation with your conciousness or change on your part whatsoever.
This applies in many fields of effort. I remember consulting with a company which insisted that only the promised following version of a particular bit of call-center software would enable them to do their jobs properly. One of my other clients had the same job to do. For that client is was executed by an experienced and painstaking man with a bunch of file cards and an excel spreadsheet.
This particular train of thought was sparked for me by a course I gave recently, my super-fast half-day GTD intro, in which a lady sat who, without being difficult about it, had already implemented the behaviors I was describing with simple tools. This was for the good and sufficient reason that she had what Dutch people call a Duo-Baan or shared job. She and her job-partner rarely met, but remained in absolute synch with each other by exchanging lists. She had knife-sharp Next Actions, well-defined Waiting Fors and a complete project list all set up in Excel and paper files. Her partner could walk in and pick up everything that was relevant immediately.
The tools are not important. Clarity is important. Completeness is important and above all Thinking It Through until it is blisteringly explicit is very, very important. If you can get those things right you could probably use trained rats and parchment to run your life.