ncShadow is a simple addon that does one thing: Adding a shadowed border to the UI window. Nothing more, nothing less! Memory usage is nihil, the file is so big because of the high-res texture. Credits to Ferous for her texture!
Install and go! Use the /shadow # command where # is a number 0-100 to set the level of shadow in percentages. /shadow 100 sets the maximum shadow, /shadow 0 hides the shadow and /shadow 50 is half the shadow. See the pictures in the sidebar. That's all, have fun!