I had an idea for plasma ZUI. The actual problem now is that you have the settings dialog on the top of the first activity and i think it's not really good because i'd like to have a preview of my activity, without nothing on top. I moved those settings on the top of the panel. I don't need to start an application while i am tweaking activities. The other thing i did is focus and resize for activity. When an user move the mouse on an activity, this activity get focus and the handle appear. The other activities resizes and "lost focus", in order to focus user's attention on the selected activity.
Mockup isn't well designed, but i hope you'll understand my idea. If you have question or better improvement, please write a comment =)