How to control your music without unlocking your iPhone

I just learned by accident today how to control the iPod portion of your iPhone without turning the iPhone on. With your iPhone off, just double-click the Home button, and a visual control comes on screen that lets you play, pause, fast-forward, rewind, and control the volume of your iPod music, with no need to slide the unlock bar on your iPhone.

This is pretty cool, because when I play music without having my iPhone connected to a power source, the screen turns off after roughly five minutes. It's also nice because if the last screen you were on was anything other than an iPod screen, you'll save time and several gestures that would normally be required to unlock your iPhone, then navigate to the iPod controls.