One of the new features in Lion is the fact that you can now resize a window from any side or corner. That much is documented by Apple. But what is not immediately apparent is that if you hold down the "Option" key while resizing a window, you get a new behaviour. With the "Option" key down the window resizes from both the corner or side that you are dragging, as well as the opposite corner or side, simultaneously. Check out the screencast below to see this effect in action. 

AuthorJehuda Saar