No doubt the niftiest addition to the Windows 7 interface is Aero Peek, a tweak to the Aero interface that lets you "peek" behind any open window. It puts the Show Desktop icon on Vista's Quick Launch bar to shame.

Aero Peek takes up residence as a small, just-visible vertical button at the right edge of the taskbar. Mouse over it and all of your open windows disappear -- you can see straight through to your desktop. However, your open windows don't entirely disappear -- you also see the outlines of each.

For example, if you have four open windows, you see the outlines of each of those screens, even if they overlap, To see the desktop with no outlined windows, click the Aero Peek rectangle instead of hovering your mouse over it. In that case, it works just like Vista's Show Desktop feature.

This does more than just offer a bit of eye candy although the eye candy is certainly nice. If you use gadgets and they are hidden by open windows, Aero Peek lets you peek through all open windows at the gadgets underneath, because Windows 7 considers gadgets part of the desktop. In addition, if you regularly keep many windows open, it's a quick way to see at a glance which windows you have open,
Switching among windows using AltTab has been improved by combining it with Aero Peek, When you use Alt-Tab to cycle through your open windows, you still display the window that you've tabbed to, but you also peek through to the desktop to see the underlying desktop, along with outlines of any other open windows, just as you can with Aero Peek.

Aero Peek is directly tied to the taskbar's thumbnail feature. Turn off Aero Peek, and you won't see thumbnails when you hover your mouse over the icon of a running application in the taskbar; you'll see a stacked list instead, You turn Aero Peek on and off by rightclicking the Aero Peek rectangle, and by checking or unchecking the box next to "Peek at desktop."