A lot of Windows 7 users miss the ‘Show Desktop’ that was available in the quick launch bar in previous versions of Windows.
In Windows 7, the ‘Show desktop’ is now placed at the end of the taskbar (see where the blue arrow is pointing towards)
When you point your mouse cursor on the ‘Show desktop’ button, the Windows 7 taskbar allows you to ‘Peek’ and temporarily view the desktop. This is done using ‘Preview Desktop with Aero Peek’. Aero Peek lets to take a quick look at open windows without clicking away from the window you are currently working on. In previous versions of Windows, without the Aero Peek, you had to minimize all open windows and then had to restore them.
Here’s a sample screenshot with the Aero Peek in action. Observe that when I hover my mouse pointer over the ‘Show desktop’ button, I am able to take a peek at the desktop without having to minimize all windows. The open gadgets are shown as transparent rectangles.
Similarly, the windows reappear when you move the pointer away from the ‘Show desktop’ button. If you ‘click’ on the ‘Show desktop’ button, the windows are minimized and you can work on your desktop. The same can also be achieved using Windows Logo Key on your keyboard + D
To enable or disable the "Preview Desktop with Aero Peek" feature, right click on the taskbar and select Properties. The Taskbar and Start Menu properties dialog appears. Check the ‘Preview desktop with Aero Peek’ section. To disable this feature, uncheck the "Use Aero Peek to preview the desktop” checkbox.