Here's what I used when I had a Palm. I'm using a iPhone now and to be honest, nothing really beats the Palm for GTD!

I originally used Agendus for viewing the NAs but any app that uses the built in todo database could be used. I modified this somewhat by using ksDateBook/ksToDo and CanDo; I've not documented this but I can if anyone is interested.

Progect Setup
=============
- assigned to the Tasks button
- four top level projects for GTD; computer, home, work, MPhil
- 'Hide done tasks' selected in the 'Project Properties'; I only want to see what I have still to complete
- each top level project has a number of sub-projects with each sub-project
having a 'Notes' section
- the flat filter is set to show only the 'unfiled' category
- each top level project has the following categories (where appropriate);
@home, @internet, @mphil, @work, date

Agendus Setup
=============
- assigned to the Calendar button
- task categories; @home, @internet, @mphil, @work, Calls (Agendus built
in), chores, date, errands
- split view shows chores, date and errand tasks (ie. only dated tasks)
- todo view is always set to show undated tasks
- list view shows @work so that I can see when work tasks have been
completed for my weekly timesheet
- todo settings; show completed items, show only dated items, record date on
completion

Using the system
================
All tasks are entered in Progect in the relevant sub-project with no date
and a category of unfiled. The following codes are used:

- '>' : waitingFor
- '<' : speak to
- '@' : email
- '(R)' : review

When a task becomes a NA, it is linked and the relevant category is
assigned. This ensures that it turns up in the correct category in Agendus.

Depending on where I am, I can then peruse the tasks for that location using
the todo view in Agendus. Due to the way that tasks are linked by Progect,
I can see which sub-project the task belongs to and I can have more that one
NA.

If a task is to be completed on a certain date, it is immediately linked
with a due-date and the category of date.

Tasks are always completed in Agendus. Therefore, when I need to review the
work that I have completed on a given date, I just go the Agendus list view
and choose the required date.


Example
=======

PROGECT
Normal List
-----------
SubProject1
Note
Note1
Note2
[]Task1 <-- NA for SubProject1, linked, category @work
Task2 <-- Task, no link, category Unfiled
SubProject2
Note
[]Task1 <-- NA for SubProject2, linked, category @work

Flat
----
Task2 <-- not linked, so is shown here


AGENDUS
@work category in todo view
---------------------------
[]Task1 | Subproject1
[]Task1 | Subproject2


If anyone has any observations or questions let me know.

Austin.