Using paper; sensitive information in your trusted device and system?
Do you put in personal sensitive information? I guess this question applies for both personal and professional information. Using smartphones and digital tools, this can to some extend be handled with built-in security mechanisms (though corporate directives may conflict with this behavior), but when using paper, your trusted device, you paper planner may fairly easily be compromised or even lost. The mix of personal and work information could also be tricky. Are you having concerns about the information you enter?
How about goals? Do you have them in your paper system you bring along? Goals on a near-runway level could maybe be considered less sensitive, but high level strategic information could pose a real problem. Jotting down personal ambition of establishing a consulting company competing with your current employer, private tax matters and investments and family issues could make me feel a bit uncomfortable. But to do GTD in a comitted way, I believe you have to be consistent on your way of working and dividing you system too much could cause some frustration.
Of course I would never ever put any password or login information in my paper based system - this would always go into a protected system like KeePass (on a USB stick for portability).