Seriously now, why do you need that super feature? When you have 10 app windows open. do you really want to check every single one until you find your wanted window?
just FYI, Win7 already has the feature you want, only slightly different.
Press ALT+Tab and you can choose there with your mouse too. (I dont know if vista had that already, i switched from xp to win7)
The new Showdesktop button is great, because you can show the desktop without aiming for a tiny icon first. Simply rush the mouse in the corner and click. Apple has a similar feature, but there it annoyed me because no click was necessary
Sometimes you dont want to loose your window arrangment, for example when you have multiple browser windows arranged for drag&drop etc.
The transparent windows, while hovering over the button, show you the active windows. This info could be interesting, because these windows will be restored if you click on the showdesktop button again, unless you opened a new window in the meantime.
Still, bottomline of all this: Does it matter? its like the "Windows startup logo Thread"