Windows 7: Use the middle-click button on your mouse and the taskbar to open a new window for an application or quickly close a window. Here's how.
To open a new window for an application, middle-click on its icon in the taskbar. For example, middle-clicking on the Chrome icon will open a new browser window.
To close a window, middle-click on its Aero Peek thumbnail. This could be useful when you have multiple windows open, since you can quickly close a bunch of them by middle-clicking. (Note for beginners: not all mice have a middle-click button, and very few laptops do.)