[jharrison]

I think task planning and task order adjustment are important activities that need to be well supported in GTD software. Most task planning probably best takes place outside of the consolidated daily/weekly review, but adjustment of task order and some creation of new tasks would be a reasonable part of the review.

The relationship between task order and next actions is important. Software that automatically links the two (the top task on the project task list is automatically the next action) may be too confining. As you note, projects may have both parallel and sequential components, and thus more than one, but not all, tasks in a project's list might legitimately appear in the next actions list.

In my current software, I create a task list for each project that optionally can be manually ordered. During daily review, I choose from this list one or more tasks to mark as next actions and then they appear in the next actions smart folder in the order that they appear in the project task list. Next actions are the "on deck" tasks for the day and I choose from that list as I work through the day. Any mix of sequential and parallel tasks are accommodated, and next actions that are not completed may, in the next review, be demoted in favor of tasks that have become more important in the interim.

This explicit choice of next actions works well for me. I like setting up next actions manually as the daily to-do list, and in the software this is done per task during a brief project review, from a quick popup menu. The potential drawback for some is that, since next actions are manually chosen, the next task on a project's list does not automatically promote to the next action for that project when the top task is completed. I don't have a problem including several tasks from a project as a correctly-sequenced set of next actions if I think I'll get to them all in one day, and the flexibility and balance between planning and action seems about right to me.