I often want to open up a 'separate' instance of a program...usually my browser when I want to compare webpages (and opening in a new tab doesn't often lend itself to this).
Prior to uncovering this little trick, this wasn't as easy in Windows 7 as I would have liked. Enter the 3rd mouse button.
I have a pretty basic 2 button mouse with a scroll wheel in the middle that also clicks.
Mouse over the application in the task bar and hit the 3rd mouse button. Voila...a new window for that application will open.