[Brian]

Nicolas, it sounds like our workflows are fairly different, but just in case it's helpful: I have exactly one single action list, for those truly random tasks that just don't fit anywhere else and aren't likely to occur more than once.

Within my projects, I rank items by priority during review: single-action-y or someday/maybe items get dragged down towards the bottom of the project.

I am a bit of a GTD heretic in that many of my ongoing projects don't have clear outcomes and will probably only be "complete" when I'm not around any more to complete them. If something languishes at the bottom of my project for years on end, I'm okay with that. :-)