Actually this isn't true, the new "Uno" model of the Arduino (as opposed to the ancient "Duomilanova") as it uses an ATmega8U2 USB interface chip rather than the FTDI chip the "Duomilanova" uses. Basically, you can reprogram the 8U2 to appear as a "standards complaint" USB MIDI device, and then it will just pop up in ALSA's MIDI tab. Neat eh?

Then all that you need to do is write "midi data" (integers) to TX... For a "hardware" MIDI port aswell as USB MIDI just solder a 5 pin DIN to the project, using the Arduino's TX pin :)

-Harry