Good, Could Use More For Serious Projects

With all these GTD apps, I can never find one that allows enough subfolders/tasks. I need: Master folder/Client/[Multiple] Jobs/tasks (which are assignable to people or groups). I love the work thats been done on this, but I cant use it seriously as a real task manager, apart from groceries, etc.

Raputznik about Producteev by Jive - Task Management for Teams, v1.3.1