Peter,
I would like to expand on this feature request. How about the ability to exclude one or more category, without having to check all the wanted categories? I just ran into a situation where I added a new category, and will have to go into the widget to get it to show. I can see where I might easily forget to do this, and my new category will be no where to be found (except on the sitemap).
It would be the opposite of what you currently have, I suppose. Or, even better, to have it automatically add new categories without needing to modify the widget. I hope that makes sense...
Rochelle