[pjb]

Allen wrote about separate piles for "waiting for" and "pending" and "reference" (that one's not really a pile but a filing system) and "someday/maybe" and there have been comments on these boards that at least "waiting for" should be a special box like Inbox but some are using Context for this. That might be "Waiting for...
---John
---Purchase Meeting
---etc as the dependencies arise"

which would allow you to Focus on that list.

Tags such as Flags, ASAP, priorities, interest are considered impediments to GTD. Janice lumped a few of these piles and tags together.

If it's scheduled, it's off your task list and into your calendar (processed).
If it's reference it's off your task list and in your file system (processed).
If it's delegated that's the same as pending/waiting on someone.
If it's ASAP then you've given yourself a stumbling block that's bound to create conflict and unhappiness (as Allen would say, as I understand him).

So we're back to having a special category for "Waiting for..." and processing everything else to either an un-prioritized action you are going to do or sending it off the task list altogether. You might send it to a tickler in the calendar to remind you to pester the person you're waiting for on some future date. "Waiting for..." can be an active task but one that doesn't allow next actions (I was tipped off to this approach elsewhere in the forum).

Sorry if this comes across as to righteous. I've been listening to the Allen audiobook in the car lately. I'm trying to grok it myself.