My implementation of GTD is a combination of both paper and electronic items. I'm wondering if this is really a good idea or not. Here is what I do, I have physical paper folders for Next Actions, Waiting For, Someday/Maybe, Read/Review.
I then have an @Projects folder on my computer that contains all of my projects. Each project is a separate Word file with a list of all the items to be done as well as the goal for the project. I have the projects as Word files, because I'm a fast typer (much faster than I can write on a pad of paper) and I can brainstorm the project. I also find that projects change and it is easier to add/remove things from a project in Word than it would be to change the project list if it were just a list of things on paper.
One problem I have with this system, is that I often have to get a sheet of paper and write down a next action for some project and stick it in my paper folder. I like having the paper folder of next actions, but I wonder if I'm just creating some extra work for myself? I'd hate to have to give up the paper though, because I often have some thought pop into my head while I'm working on something on the computer, so I stop for a minute, write it down on a piece of paper, toss it in my inbox and continue with whatever I was doing. I find myself catching much more stuff this way that used to fall through the cracks.
Another thing, is that I also have 2 lists on a Palm. I have a calls list and an errands list. I decided to put this on my palm, because these things I can do at home, work or when I'm on my way somewhere else (errands).
I guess I'm feeling like having 3 separate places for my lists might be a little too much, but it has been working well so far.