In case anyone else is interested here is what I am trying to do for GTD using Leopard Mail and a Palm TX. Bear in mind that previously I have been doing GTD on the Palm using lists created in the Tasks/ToDo's much along the lines of what David Allen suggests.
So the ToDo's which are context related all carry across to Mail. Each context is a calendar. I have set up a Note for each Project (or Pending or Someday/Maybe) and recreated the ToDos so they are written on the corresponding note and you then have the link back from the ToDos to the Note. As you can turn off and on the ToDoness of any bit of text in the note I have the notes setup up as lists of actions with the n/a a To Do. Links to material and other supporting stuff can also go on a note.
How to review the ToDos as reviewing them in iCal is cludgy and was before Leopard. You can look in the ToDo mailbox and sort by calendar to see them by context. This is like having a list view of ToDos in iCal. A better solution would be to have a smart mailbox for each category. I tried this and there are bugs I hope will be resolved in 10.5.1.
How to get Notes on the Palm ? The Notes don't sync to the Palm. The guys at MarkSpace who make Missing Sync say they are planning to have a look this but right now they are busy making all their Missing Sync applications Leopard compatible. So I went via the email route. The Notes sync to my IMAP server and I can look at them in VersaMail on the Palm TX. But now there is a catch. VersaMail won't look inside nested folders on the IMAP server and I have a GTD folder with Projects, Pending etc sub folders. So I am trying out Agendus SSL Mail at the moment which does handle folders and looks quite good.
There are some cludgy things: I haven't sorted out how to create notes on the Palm and sync back via email and the notes when you create them on the mac have to later be dragged into projects from the Notes folder.
A work in progress but it is interesting what you can do.
PS: Yes I know messing with one's GTD implementation is not `getting things done'