Unlike all other iPods up to now, the new shuffle doesn't have the volume and playback controls on the body of the device itself. Instead, the controls are located on part of the earbud cord itself. (There is a switch on the device for changing from shuffle to straight playback mode.)

Tinkerers who dissected the tiny control module found a chip inside with an unknown purpose. (The same chip has been found in the iPhone Stereo Headset that comes with the latest iPhones.) It may just be part of the control system, or -- some worry -- it may be required for the shuffle to authenticate the headphones.

In either case, it theoretically gives Apple control over what 'phones can be used with the shuffle. It's possible that the company could restrict the shuffle to Apple-brand earbuds, but it would be more likely for Apple to use it to extract licensing fees from third-party manufacturers. 

On the other hand, it may just be a straightforward part of the control mechanism that other vendors could easily reverse engineer without repercussions.