Cranking Widgets Blog has a wonderful post, A Roadmap to Spectacular GTD Failure, that, as he puts it, "if you want GTD to over-promise and under-deliver, follow these simple steps…" I think my favorite one is:
Make sure your filing system consists of unholy amounts of papers and crap strewn around your entire physical life - My office is too full of stuff to make room for a filing cabinet! I’ve had this “unorthodox” filing system for years and it’s only let me down… well, a couple of times. But who has the time to organize when you have as much stuff as I do!
I try to practice GTD, but I have been allowing too many distractions to come in, I have let my email become my filing cabinet, and I have not done a review.
I have been cleaning out my email off-an-on all weekend and still have over 700 to go. This is crazy and I have been finding tasks that I have forgotten because it wasn't captured in my system.
I need to do better and keep at it. I found when I was capturing everything, I was more productive and kept up on everything. When I let it lax, I started missing stuff. The point, keep up with the system. It works.
Let me know what your issues are in making sure everything is captured and how it works for you.