Snow Leopard - Enhancements and Refinements
Dock\Activate Exposé from the Dock.
Click and hold an application icon in the Dock, and all open windows in the application you selected will unshuffle so you can quickly change to another window. Press the tab key while in Exposé to move to the next application in the Dock and show the windows for that application. Minimized windows appear as smaller icons below the other windows. And windows are spring-loaded, so you can drag and drop items between windows.
I have the latest developer seed of Snow Leopard (10A354) and it doesn't seem to have this feature..? anyone know if it's just not been implemented yet? Tried it with a few Safari windows open and it just shows the right-click menu like normal when you hold down the icon..