I doubt I have implemented any of this well as it was just a quick weekend hack. But it addresses a number of things that have bothered me about the Properties Editor, especially through the eyes of new users. But perhaps this could provoke some discussion...
First, the order of the items in the Properties Tab list is changed to what many people have mentioned to be a more logical order.
Tabs are separated into four logical groups rather than three, so each section is a smaller, and more visually manageable, group.
The group separators are larger (just uses two each rather than one), so the groupings are much clearer to notice. The current separators are too small to do the job.
The breadcrumb is now only showing a single endpoint of the path, so only the object acted upon. The current breadcrumb is confusing and not very useful to be honest.
The header now includes a title, which many new users just expect to be there.