You can also get two screens plugged into a Windows machine, and extend your desktop across both screens, which means I can run one application on one screen and another on the other.
What I'd quite like at the moment is to have one screen logged in as me, and the other screen logged in as an Administrator (or another user), and to switch sessions by sliding my mouse from one screen to the other... and Windows can't do it. I have to keep switching users, and I can't look at both sessions at the same time.
Boo to Windows!