The possibilities with Android keep surprising me.
Last weekend I turned my mobile phone into a metal detector!
And today I discovered I can actually debug my application on my HTC Magic device through its USB cable. Just plug it in, install the ADB USB-driver (from the Android SDK), launch Eclipse and start the application on the device. From Eclipse you can connect to the application that's running on your device, but make sure that it was built with the debug option enabled, otherwise it won't show up in Eclipse.