Android developer and all-round technologist AdamOutler has published a series of video tutorials on creating Android apps, and also integration with the hardware via the Android ADK. Starting from basically blinking an LED he takes you through a variety of topics to the point of home automation and other useful system ideas. The videos are well presented and make interesting viewing, for example:
If you're looking for an Arduino-compatible board with inbuilt USB host shield for ADK experimenting look no further as we have the Freetronics USBDroid board:
Apart from being a fully Arduino Uno-compatible, it has onboard microSD socket and the full USB socket and host-mode controller. As well as the Bluetooth application described above, this is the ideal platform for developing peripherals or projects based around Android devices with ADK (Android Developer Kit) functionality, but without requiring a USB host controller shield stacked onto an Arduino. For more information and to order, visit the product page here.