I've just read GTD and have already noticed an increase in productivity and a decrease in stress.
One thing I'm struggling with is the following. I spend periods of up to several hours each day deeply immersed in what I'm working on (which is programming stuff, but it could be anything that requires abstract thought). During this time I'm very concentrated on what I'm doing and following a delicate train of thought. Then suddenly (for example) someone will need to talk to me about something. I'm aiming for a 'mind like water', whereby I could just stop what I'm doing and give this person 100% of my attention. But when I've been deeply immersed in what I'm doing, I find it very difficult to suddenly change my focus completely to something else, and normally can't give this person the complete attention I'd like to give them. It's like my mind resists letting go of the task I was working on before it's complete.
I suppose one solution might be to very quickly capture my thoughts at the moment of the interruption so that I could pick up where I left off. The problem with this is that the tasks I'm working on can be quite abstract, and difficult to express using a quick note.
So my question is, when you have a 'mind like water', allowing only the task at hand to be stored in your mind, what do you do with the contents of your mind when you suddenly have to change tasks?