I used to use GTD, but nowadays I mostly just use the "capture" part, a.k.a
LET IT GO OUT OF MY SYSTEM DAMMIT. The remaining steps just sort themselves out as things are falling into very different buckets: a. very general life goals (non actionable by themselves due to their large scale, virtual nature, and can only be achieved by habit as well as internalising what I truly want, but certainly
not with reminders), b. whatever I fancy doing when I happen to have some free time (for which I may go back to a quickly jotted draft of step 1, and since I'm in the mood for it, well, I just do it), c. very concrete errands and other mundane tasks.
GTD is a worthy attempt at formalising things but in doing so it's way too generic and thus doesn't pragmatically cater for the very different situations above. IOW theory and practice are the same... in theory.