I've been using org-mode for a while now, and I really love the way you can use tags for multiple contexts. It seems that multiple contexts is a big point of discussion among GTD app people, but for me it's great to be able to see something I can do in any place or mindset I happen to be in. If I need to get in touch with someone, it could be on their agenda, and the contexts phone and email at the same time (yes, I know most people prepend '@' for contexts, but in the book that was only a hack to get these things to list first in certain GTD-unaware apps like email clients).

The pretty much free-form way you can structure the files and link between them can fit just about any way you like to work. I put my small projects (2-7 steps or so) into one large file, keep the larger projects and my thoughts and ideas about them in their own files, and simple NEXT actions in their own files. I can link to all these from a master file for easy weekly reviewing.

If any emacs user out there doing GTD hasn't tried org-mode, I urge you to do so at your earliest convenience. If you have a recent version, you don't even have to install anything. Once you get used to it you might want to upgrade to the lastest version, though.

I found the agenda view a bit unwieldy if you just want a certain context list, however, especially if you want to print it out, so I wrote a little shell script that looks through all the .org files and spits out a little checklist of the context you want to see. It keeps me sane.