This is so cool it is almost insane! And this will definitely increase the usefulness of an already extremely useful device beyond what anyone can dream of today.
Android 3.1 SDK new Open Accessory API
The new Android API, primarily for tablets (let’s hope it will be used on smartphone devices soon as well) means it will be much simpler for hardware manufacturers to connect peripherals to your Android device.
The API allows any device with host USB functionality to connect to a multitude of USB devices and interact with many different kinds of devices from music devices, exercise equipment, input devices such as joysticks, standard USB keyboard… you can almost find no end to the stuff that you could potenmtially hook up to your android.