Nat: Those Mezzo mockups are pretty neat. I think I like the idea of hiding all the windows as you open the documents dingus. You could really go a good job with the animations that Xgl would make possible there. The so-called menagerie bothers me, though, because by being on the desktop, behind all windows with no way to bring it and only it forward, it requires the user to reorganize his windows around it. It’s the same problem I have with removable media icons appearing on the desktop in both OS X and GNOME.
I’d love to see some data out of the testing Anna and Pete did on how people use the desktop. I always have a million windows covering it, so I find it to be completely useless all of the time. I much prefer the omnipresent panel/dock, and I wish that icons would appear there rather than my panel when I insert a CD or plug a thumbdrive in. OS X makes this a little easier with Exposé, but it still requires an unnecessary keypress, and can be very difficult to use with drag-and-drop. I think the perfect demographic for this is middle school girls, because they have at least one browser window and a million instant messenger conversions going at once. (Maybe once they get to that point they have no reason to open anything from the desktop, though.)