Hmm, I guess there's probably a worse language than XML to use for specifying 3D representations, but I can't think of it.
Well, perhaps AmigaBASIC :-P
I've got halfway through this video but I've still yet to see a decent use for a 3D representation for the average application. Previous demos of Longhorn, with windows 'waving in the wind' when you moved them just seemed like the most pointless waste of system resources. How does a window waving around when you move it actually of any assistance to anyone?
I've never seen window translucency of any sort come in handy when it comes to multitasking. It just makes both the foreground window and the background window hard to read.
If you're going to change how the average UI works in most GUIs, you need to change the whole model of thinking. I don't see how a 3D respresentation on a 2D surface is ever going to be of any use to anyone (in terms of apps usage).