The trick is figuring out the good tree-top to go to as a starting point, which is not easy because it depends on your goal and you also need to be fairly familiar with the category tree and naming conventions to begin with.
Yeah, navigating down isn't so much the problem. It's the navigating up that's tricky.
I think having a [+] besides the categories listed at the bottom of the page might help - it would work like the dynamic tree on category pages, but "up", not "down". The code is actually there, the problem one of layout: I have not found a way to implement a flowing line of things that can expand to complex blocks, reliably, for all browsers.
I may look into this som more in the future. So much to do - I have to check priorities with WM Germany :)
-- daniel