I've tried GTD but no one tool works for me and I end up falling off of the wagon. Email is usually my downfall. I'd prefer everything on paper, whether Moleskine notebooks, index cards, or just folded printer paper. But taking an incoming email (that will take more than 2 minutes to act on) to a task on paper is usually such a heavyweight process that I never do it.
So I end up trying to manage everything in my email+tasks systems (Exchange/Outlook for work and Gmail for personal). That works somewhat well, but breaks down for a couple cases. I still prefer a paper list where I can scribble new input as well, for meetings and offline / distraction-free planning time. It's not as hard to copy from paper to email+tasks, but I never seem to get it done.