I have a couple of suggestions pertaining to folding items in TP3:
The bullet icon is a very small target, making it difficult to click on. I often miss when I try to click on a bullet and end up having to click a few times to finally hit it. Also, the bullet icon is non-intuitive, in terms of representing its intended behavior. I think it would be better to use disclosure triangles that face right when collapsed and rotate downward when expanded.
I use multiple levels of projects and my sidebar is becoming cluttered with too many sub-projects and sub-sub-projects. Would you consider implementing folding items within the sidebar?