Yep, paper-based is working well for me...
I've been using GTD for about two years now and recently switched to a paper-based system for a number of reasons.
My partner used to (well, still does) make fun of me for always getting organized, yet rarely making progress on getting things done. (That's not entirely true, but it looks that way from the outside.) I realized a few months ago that I frequently look at other applications and test them out to see if they're better than Toodledo. I've wasted a bunch of time setting things up in other systems, trying them for awhile, then reverting back to Toodledo. In retrospect, I was just procrastinating and playing.
With a digital system, I often wrote paper notes while on calls or in meetings because it was quick or I didn't have access to the digital system. (Typing a long note on an iphone is tedious for me.) Later, I'd have to transfer those notes to the digital system. Usually, I'd be overwhelmed with new stuff and those notes just wouldn't make it in the system, so I couldn't trust the digital system to be up to date.
Less detail/more focused/less duplication
It's so easy to copy-and-paste with my digital system that I ended up putting way too much detail in it. Copying entire e-mails that required me to scan lots of text to get the gist of what the task really was - annoying. With the paper-based system, I just write out a few things - sometimes "Issue 363 - fix user access" because that issue was already logged in the clients SharePoint site, so I could go there for the details (which would also be more current than my list).
My paper-based system uses small notecards (about 2 inches by 3 inches) and a little box with dividers. I keep a stack of notecards on my monitor stand and just grab one whenever I have a new task. The small size forces me to be brief. Since I still have some tasks which require additional detail, I have OneNote on my computer that contains reference material. The cards are great because I can lay them all out and see a global picture of each context or group.
When I'm out and about and think of a task, I just send myself an e-mail and write it up when I get back to my desk.