I've been implementing the system for a couple of months now, and I feel like it's going well. I browse this forum, 43folders, gtdwannabe blogs, etc. and in the midst of all of this GTD discussion, I've realized that I haven't heard from anyone that says "I've used GTD and am in the zone, and it's great."
Of course it makes sense that the people actually in the zone aren't wasting their time browsing through the web forums. But if you read even the coach's corner articles on davidco.com, THEY mention their problems with the systems too. Merlin of 43 folders mentions how he's terrible at it, that's why he obsessed with it. This has all led me to wonder, WHO besides David Allen himself is actually IN the zone? I'm not talking "well, this system has really helped me". I'm talking "stress-free productivity baby, yeah!", with emphasis on the stress-free part.
As for me, I think the system is going awfully well right now, but I wouldn't say I'm totally in the mind like water zone. Maybe I feel close, so that is why I'm writing it, I don't know. Lastly, if anyone says "you can't ever get there, you can only approach it" I'm going to be sorely disappointed. Not at the realization that it doesn't exist, but disappointed at the lack of optimism in that statement. I think what David talks about in the book is possible, I just want to hear from people that feel like they've sustained it.