Your 30 Day trial has intrigued me and has made me want to try my own experiment with a paper hybrid system. I have been at GTD for almost a year now and have been using primarily electronic lists managers (Palm Desktop to Outlook to now Lotus Notes) to track next actions, waiting for's, projects, etc. as well as managing my contacts and calendar.
What I find is that initially my list management works well, but as time passes, I struggle to keep my next actions and project lists meaningful and up to date (even with weekly reviews). This becomes particularly problematic when things get really hectic, like the current stage of my project where there are multiple fronts and associated next actions that must be tracked in a very short timeframe. During these times, I revert back to simple paper to do lists of next actions and find that I am able to better focus on them during the day.
The problem when I do this is that I now have next actions and project lists on both paper and electronically. If there is a "lull in the battle" or during weekly reviews, I try to type all the paper next actions and projects back into my electronic one. It feels very inefficient, but at least for a moment in time, all my things are on one list manager.
Perhaps, subconsciously, I am trying to tell myself that my preference is to work on paper lists. I have resisted going more to paper up until now since I like the convenience of key word search and security of easily backing up of my electronic versions.
I think I will give the paper / hybrid version a try for a few weeks. I read your blog for some ideas. Let me know if you have any other key tips, especially after working your hybrid process for a few months now (?)