This is my Idea for a combined Task Switcher and Desktop Switcher (Pager). This is not a completed app. Notice the two alternative approaches and the different ways the gimp is handled on Desktop 2
When you hit Alt-tab you would be presented with something similar to the screenshot above. The largest bar contains the documents associated with the current desktop. Just as normal, hitting Tab will cycle through these documents and releasing Alt will switch to the selected document.
-Using either the arrow keys or mouse it would be possible to switch to any document on any desktop instead of just the documents on the current desktop.
-Dragging and dropping of icons onto different desktops. This would provide a visual way to manage virtual desktops.
I would personally find this very useful, and it seems others would too. It's a useful feature no other desktop environment has.
Things to consider further:
-How could multiple instances of the same app be handled to make quick identification easiest. (there is probably a better way than the way I've shown.)
-How to treat stickied apps.
-Visual style: I've drawn heavily from the Mac Command-Tab aesthetics, but there might be some subtle ways to improve the feel
-Using window thumbnails this could be the start of a sort of ZUI.
-There are definitely more things to consider...
Please email me if you are interested in developing this idea.