I've just tried to start moving from my current GTD system - Vitalist - to the Doit. I've spent just 5 minutes working with it until understood that I won't be able to move to the new system. The cause is simple - Doit doesn't support subprojects. Currently, I have dozens of projects grouped in a tree-like style, which I find very useful approach. But I'll struggle to copy all my projects and tasks using available features of Doit. What a pity! It seems like I need to find something else to use...