I was asked to play a small concert at my friends PhD defense using an Arduino running this library.
Listen to the result here:
The music was sequenced using Ableton Live and sent to the Arduino via. MIDI @ 31250 BAUD serial data. The output from the Arduino was a 8 bit PWM signal that was subsequently lowpass filtered using a simple LC filter.
Part of the low pass filtered audio signal was sent back through a echo effect processor (inside Ableton) to add a bit of flavor and make it tolerable to regular people :)