For me, tracking projects has always been the hardest and most intractable part of GTD. In particular, how to manage future actions and keep track of sub-projects I've delegated to others.
I've toyed with documenting next actions in a project list and appending a project titles to tasks, but I struggle because with small, quickly accomplished tasks the list thrashes so much it's hard to stay on top of it. I just never feel like I have a good home for future actions or a canonical place to keep my in-work projects.
Sub-projects assigned to others
If I've asked someone to do a specific task it's easy enough to put in a
waiting for context list in RTM. I struggle when I've assigned someone something that's a project in it's own right, but only a sub-project within my scope. I can track specific actions I've given them, but don't have a good way of being able to quickly see their progress towards the larger goal and ensure they're focused on the right things.
I've heard a little about Trello and it seems like it was designed for this problem: it resides above the bug/task level and does more for tracking projects, but I haven't really experimented with it because I'm not sure where to start. Has anyone developed a good Trello workflow and figured out how to integrate it into a GTD system and task tool like RTM?