Much like the window preview provided by WindowFX, it'd be very cool to hover over your virtual desktop selector in the taskbar (maybe an icon, if that gets implemented), and have a row of icons or window previews display.  The effect could be similar to how ObjectDock can display a folder's contents, though for this I would consider making the display a straight bar just above the taskbar, and scaled to fit the icons or window previews of the virtual desktop in question.