I use ShadowPlan on my Sony Clie for my next actions as follows:

Parent level is context
The child level is either NA (if it's a stand alone) or the project name
If it's a project the NA for the project goes as a child/child level.

When the next NA in a project changes context I can easily move it in ShadowPlan. I originally used Tags in ShadowPlan but have found it easier for me to work this way.

I use Datebk5 for my hard landscape and tickler files.