[SpiralOcean]

I'm not using OmniFocus yet, but let me see if I understand what you are trying to do.

You want a projects actions to be on hold, or invisible, because you are waiting for so and so to do something.

You can accomplish this with contexts.
You created a context for waiting for: Joe
Now you need to make your project sequential and make sure the task for joe is at the top of the list.

This will hide all other tasks until you check off the task associated with joe.

I'm assuming OmniFocus is allowing the sequential/parallel switch based on a task and not on an entire project. If this is true... here is how you would set up a project to automatically become parallel after the waiting for item is checked off:

- paint house: sequential
--call Joe about painting: waiting for
--Paint the house: parallel
---paint northside
---paint south side
---paint east side
---paint west side

once you have what you are waiting for from joe. the other 4 tasks should show up in their respective contexts.


Bushford:
I don't know where the contention comes in for contexts. If you have read Getting Things Done by David Allen, you will see that Allen has a context called waiting for. In the context he will put:
wf Joe to call me about tools
wf Susan to get materials

Contexts are not about place/time, but what tools you have avalible to you, which could include a place/time.
I am near a phone... go to the phone context
I am at the grocerystore... go to the grocerystore context
I have 10 min before my meeting starts and near a computer, what can I complete in 10 min.

Filtering for deligated actions is the same as filtering for deligated contexts.