Apple has patented a dock that allows for users to chain their iDevices together. The description is as follows:
A system for communicating between an accessory and an electronic device includes a first interface, a second interface, and a docking station. The first interface is configured to communicate with the electronic device. The second interface is configured to communicate with the accessory. The docking station is coupled to the first interface and the second interface. The docking station is configured to receive a set of preferences from the accessory and forward the set of preferences to the electronic device.
The idea is daisy-chaining devices such as two iPhones or two iPads, and is probably designed for easy data transfer between your iDevices. Perhaps you have photos on your iPhone that you'd like to put on your iPad (or vise versa, once the iPad 2 hits in it's camera-equipped glory). This may also be explaining little more than something like one of those iPod speaker systems with the dock and built-in controls. It's a lot of talk about interfaces and accessories, and patent application wording is usually far from clear. Still, it's just another look of the kinds of ideas that Apple plays with back in Cupertino.