Hey, I replied elsewhere too, but since I am doing research on the topic, it seems http://adrianfreed.com/content/oscuino-arduino-osc-sketch-open-sound-control-work OSCuino is the most efficient firmware.

The OSC is wrapped in SLIP packets and I cannot unwrap it in e.g. Puredata, Processing.
At the bottom of the page, Freed supplies a Max patch, however I am running Linux now and cannot try it out. Any suggestions about that? Should I use some intermediary script that unpacks?

Look for "Arduino knock sensor" (the forum doesn't allow me to post links because it is my first post :\)

@matt, I am also researching this topic and it seems that the most efficient OSC firmware is this http://adrianfreed.com/content/oscuino-arduino-osc-sketch-open-sound-control-work
however it works better on Sparkfun Bitwacker and CREATE USB boards, because there it supports bundles, timing, etc.