Well this is neat.
I just found a nifty little feature in Windows 7. If you middle click on an item in the task bar it will open a new instance\window of that same program. For example, if you middle click the taskbar button for a firefox window it will open another instance of FF. If you middle click a windows explorer window it will open a window showing your library.
I don't know if I'm going to ever use this but its pretty neat.
Though I think I'd rather have middle click close a window like it does with the tabs in Firefox.
EDIT: Sweet! Someone actually made a program that allows you to close things by middle clicking the task bar icon...