Selecting grouped windows with a mouse is highly inconvenient. Let's say I have two firefox windows open and I want to select one of the two with a mouse. I have to click on the firefox launcher then possibly move the mouse across the screen by a distance, depending on how many instances are open and which one I want to access, then click on that. In Windows 7, thumbnail views of the open windows are shown right next to the launcher, which is way more convenient. I am even fine with if only some text, instead of thumbnails, are displayed next to the launcher.