In Windows 7, in the extreme right side of the taskbar, you will see a vertical rectangular portion.
Moving your cursor to this area will make the open windows transparent and let you preview your desktop. Clicking on it will show the desktop. This is called as the Desktop Preview feature in Windows 7.
But if you dont like this feature or hardly ever use it, you can always disable it.
To disable the Windows Preview feature in Windows 7, right click on the taskbar and click open Properties.
Under the Taskbar tab, you will see a checkbox to Use Desktop Preview. Un-checking it will disable this feature. Click Apply > OK.
Incidentally, right clicking on the Desktop Preview button will also present you with this option.
Windows 7 offers many new features. It will offer improved navigation, a new task bar and a streamlined UI so that common tasks done in Windows are done easier and more quickly. You will be able to share data to all your PCs and devices in your home network or at work. With Windows 7 + Windows Live, you will be able to stay connected to the people that matter to you, and with Internet Explorer 8 you will get a faster, safer, more productive Web experience. Along with Touch Gestures and Device Stage, Windows 7 enables you to get more out of your devices including the ones you use most often like your digital cameras, mobile phones and printers. Windows 7 makes it easier to use networked media devices to play music, watch videos, and display photos that are on your Windows PC.