Reader Ace writes in with a nifty customsation that will set your Mac apart from the rest. Find a desktop wallpaper image (Social Wallpapering's a good bet), save it to your desktop as background.jpg, and in the Terminal type:sudo cp background.jpg /System/Library/CoreServices/DefaultDesktop.jpg
You'll have to enter your password to complete the operation, and when you do, next time you log off, your logon screen will have your new custom background. Slick. Thanks, Ace!