7 Taskbar Tweaker gives you more control over the Windows 7 superbar
Why not set your middle mouse button to close using 7 Taskbar Tweaker? By default, middle-clicking a superbar icon in Windows 7 opens a new instance of that program, the same way shift +left click does. I don't need to do that very often and holding shift really isn't an inconvenience for me.
On the flip side, I close windows and tabs from the superbar all the time. Right click -> close all windows works, but why not make use of your scroll wheel's clicking ability?
Taskbar Tweaker also allows you to change other superbar click actions. Another change I've made is swapping the default left click to open previews to cycling through windows/tabs. It's a welcome switch if your web browser happens to support per-tab thumbnails.
You can also use the app to disable thumbail previews if you choose, and the settings menu provides options to run at startup, hide the main window, and even hide the tray icon if you like keeping clutter to a minimum.
7 Taskbar Tweaker is a free download and versions are available for both 32 and 64-bit Windows 7.
Thanks for the tip, Miklos!