I've finally taken the time to port MicroBridge to the Arduino/Wiring language. You can use it to make Arduino and Android talk to each other over USB. This is like Google's open accessory toolkit, only it uses a different protocol (ADB), and therefore works on any Android device version 1.5 and up. The phone or tablet does not have to be rooted, and you don't need to upgrade to 2.3.4.
Read more about it here:
http://romfont.com/2011/05/15/microbridge-adb-support-for-arduino/Google code project page:
http://code.google.com/p/microbridge