I think more importantly than having folders determining URL's is what we do with User Controls. Because I may have a BlogPostController, it has actions for New, Edit, and View. So New and Edit are /admin prefixed and View may be /BlogPost/2009/09/12/this-is-my-slug
I think the URL specification should be higher priority in the chain maybe. To me it doesn't matter if it is conventional or not because we are having to configure something on 98% of our Url's/Actions
Problem I have, which we alleviated somewhat is that I can put controls that are used by ControllerA into A's folder, but I can't use those anywhere else on another controller. So still my shared folder has 95 controls in it, just so I can use them in different controllers. I don't know what we could do, but it would sure be nice to be able to logically organize all these files.
I can't remember right now how Fubu goes out and finds controls and views, and I don't think we want to box ourselves in to strict on a "Required" Folder structure.
-Ryan