Good perspective on "falling off the wagon" with GTD over on "Open Loops", particularly with regard to assessing where you are. I find that you're never as far off as you think, but that doesn't always make it easy to get back on the path.
The advantage of following these methodologies is that there are a lot of kindred souls to learn from.
I'm reading yet another couple of books that I think can add to the "community of practice" on this. Will be finishing them up on a cross-county trek tomorrow, so look for a summary by the weekend.