Hmm, I don't know, I find 4 virtual desktops on GNOME both enough and almost confusing already. And those are 2x2 grid instead of 1x4 grid. In the 1x4 grid of Maemo/Panorama the desktop of preference is always max 2 swipes away. However if you'd want say 6 virtual desktops a cube model might be an option. In such case, it is also max 2 swipes away, and the 3D model helps to envision people what is where. Except such costs quite some time to implement, and one can swipe the wrong way which is not possible with 1x4 grid.