The Inactive Widgets area is so that if you remove a widget from a sidebar but don't add it to a different one, you can save it with the settings in the Inactive area. Since the widgets are all multi-use, it wouldn't have worked to just drop the settings back into the main list instance, b/c if you had, for example, 3 text widgets that you were temporarily pulling out of sidebars and you wanted to save the settings for all of them, it would be confusing. So the main list at top left is default widget settings, and Inactive is to save widgets you're giving a time-out.

And no, we haven't done any of the styling yet. It will come. :)