The ability to dock a given window to for example the left side of the screen and then set it to auto-hide so that when the mouse touches the left edge of the screen the given window slides out to become visible and when the mouse moves away outside of the window the given window hides itself by sliding back down to the left edge of the screen.
This would be ingenious for screen real estate. For example a buddy list messenger window or a notepad instance or a calculator could always be there with no clicking required to bring it up, just simply hover the mouse and touch the edge of the screen to slide the window out and into focus.
Please consider implementing this. I personally haven't found this anywhere else and it would be timesaving invaluable feature.