Here's a cool application made for Windows 7 that changes the way the taskbar works in two ways. The first is that, by default, if there are multiple instances of one application open, a single left click on the app's icon displays the thumbnail previews of all the windows in that application, and an additional click on a thumbnail restores the window. Taskbar Overlord changes it so that a single left click on the application's icon in the taskbar restores the last active window of that application. The second change is that, by default, middle clicking the icon of an application opens a new instance of that application. Taskbar Overlord changes it so that middle clicking the icon closes all instances of that application (a new instance can still be opened by Shift+Left click).