In Lion you can resize most windows by grabbing any edge and dragging. But if you hold down modifier keys you can make resizing behave in different ways. A regular drag on an edge will move only that edge. Hold down the Shift key and three edges will resize, with the opposite edge remaining steady. Hold down Option and the current edge and opposite edge will move. How down both Option and Shift and all four edges will move, with the center of the window remaining fixed.
Mac Video Tutorials and Tips for Apple Users
