I have been watching music mobile apps that harness accelerometer and gyroscope for a while. Many of these implementations have been pretty clumsy and toylike rather than offering a serious expression alternative that a serious musician/DJ might be tempted to use. This new $20 AirJ is looking really powerful. You can see it in use with Ableton Live here: Sonic State – News (Video Item) BPM10: AirJ App Transmits Native MIDI Over Wifi
Put your hands in the air and trigger something.