Click on the image below to view it full size in an image viewer !
KDE3.5: Desktop Pager: floating widget with overview of desktops and window positions

Shows a snapshot of the KDE Desktop Pager application with multiple named desktops, as a window is being moved off the right edge of one desktop to another.

In Mac OS Leopard Spaces it seems one has to go to F8, which does give a nice full-screen view of all spaces. Is there also a mini overview like the KDE one above ?