This was my experience. The question I had were surprisingly hard to answer.
1. What is GTD and does it work? 2. If GTD is failing for me is it because I am not doing it wrong? 3. If GTD is failing for me is it because my implementation is wrong (i.e wrong tool or badly designed app)
The problem with the GTD system, as much as I have enjoyed using it, is that there is no reference system to verify correct usage. The usual path taken, for those who are patient and motivated, is that of hacking your way through the books, tutorials and apps out there until it feels right. The 'it feels right' feeling comes if you actually feel like you are on top of your work load. The system you end up with that works for you (when you eventually get to this place), may look very different from what the book described or what you initially envisaged.
GTD is more like meditation than a system. It's hard to learn it by reading about it. You only know you are doing it right when your life feels lighter and more productive.