Love them or hate them, you have to admit that Apple is always looking at new ways for users to interact with their products. Sometimes it works and sometimes it's a dismal failure. I'm looking at your puck mouse.
When Apple discovered that its users were listening to music on the random setting of their iPods more and more often, they capitalized on the behavior. They and introduced the iPod Shuffle. A small, lightweight and cost effective way to listen to music randomly, at the cost of a visual interface. Great for gym bunnies, joggers, people with one song in their music library, and not much else.
The iPod Nano fits in between the Shuffle and a full sized iPod, supplying a screen big enough to interact with but a form factor small enough to go unnoticed in your pocket.
The little difference in this generation of Nano is the ability to quickly switch to a song at random. There's no fumbling through menu items or searching for the right button to push. You simply shake the device and it does the rest for you. An interesting interaction; taking the mental metaphor of "shaking things up" and translating it into a physical equivalent.
This adds a certain "wow" factor to the device that is sure to be shown off to friends and family. Its nice to see Apple continuing to add features to the iPod, instead of resting on its laurels.