Google is now offering Android 3.1 Honeycomb SDK that brings quite a few API changes out of which most revolve around USB host and USB connectivity. This includes the just announced the Open Accessory system as well.
Here is an excerpt from Google Android developer page (download link on that page).
A USB device is a piece of connected hardware that depends on the Android-powered device to serve as host. For example, most input devices, mice, and joysticks are USB devices, as are many cameras, hubs, and so on.
A USB accessory is a piece of connected hardware that has a USB host controller, provides power, and is designed to communicate with Android-powered devices over USB, A variety of peripherals can connect as accessories, from robotics controllers to musical equipment, exercise bicycles, and more.