For today's Mac 101 I thought I'd draw your attention to a feature of the Displays tab of the System Preferences that only appears on external monitors: Rotate. If you plug in an external monitor to your Mac you should see that you have the option to rotate the display by 90 degree increments (clockwise). Now why would you want to do this? Well, if like me you have an external widescreen display, sometimes it's actually more handy to use it vertically instead of horizontally. I do this because I work entirely on the main (24") display and use the external (20") for showing my email, iTunes, etc. On my desk, I feel like this is a more efficient allocation of pixels. You can see a picture of my setup after the jump.