I like this tip since it offers you a quick and easy method for viewing the windows belonging to other apps without loosing focus on the current app you are using.
The mouse pointer has special powers when you use it to hover over an apps icon in the dock, but those powers used to invoke App Exposé only come to life with a four-fingered downward swipe on your trackpad.
Completing that gesture while hovering over an apps Dock icon in Mac OS X Lion causes the OS to show all the open windows for that particular app. The windows for the app you are using aren’t displayed.
If you make the four-fingered swipe in an upwards direction the current window view reverts back to the app you are using hiding the open windows for the app in the Dock.
