Here are a few more of the useful tips that I found in the PC World article "50 Essential Windows 7 Tips".
Hidden Wallpapers - go to c:\Windows\Globalization\MCT to find wallpaper images from all over the world that you can use to customize your desktop. One of the things that I like about Windows 7 is that it's easy to set up a set of images from any location ("my pictures" for example) to be used as wallpaper and that rotate automatically several times a day.
Change the launch folder for Windows Explorer - it defaults to the Libraries folder which is not useful to me. You can change this by right clicking on the Windows Explorer icon and using the Properties function. Edit the Target field with a new folder location to change the default when it opens. You can also "pin" a shortcut to the Windows Explorer icon, so that when you right click on it, the pinned item is available on a list similar to "recent items".
It is very easy to "pin" programs to the taskbar that you use frequently, so I find myself using those icons all the time rather than trying to return to my desktop icons.
You can also customize the image that is used as the background on your login screen. In order to do this, you have to make a small change in your Windows Registry file, so I don't recommend trying this if you're a novice user.