Some interesting stuff here guys. For interest - here is my system in TD:
The biggest driver for me is that I set it up so that I can see what I want on my iPhone, which is a lot less flexible than the desktop version. I want to be able to see my next actions for work, and my next actions for personal quickly and separately.
I use the following folders:
@next actions - personal
@next actions - work
Non-urgent - personal (this allows me to 'defer' less urgent next actions and allow me focus my time)
Non-urgent - work
Project - personal
Project - work
Research to do (I like finding stuff out so keep this separate)
I also have an 'inbox' folder which is the default entry for new to-dos.
I use contexts only where it gives me another option:
Agenda - boss
Agenda - wife
This allows me to check what I need when I'm in the shops, what calls I need to make if stuck waiting for a plane etc.
Projects have sub-tasks, but only tasks that are next actions.
What do you think?! Seems to work for me - not perfect but best way I can get it to work on computer and iPhone.