http://arduino.cc/en/Tutorial/MidiThis works, I have made MIDI controllers with it and its fine. the issue is that you get non usb based MIDI so u need a MIDI in for the computer.
Eek. That may work because of tolerant hardware, but it's definitely wrong. The MIDI interface is a current-loop one and that tutorial is voltage-driving it. On the transmit side the worst that's likely to cause is that it just plain won't work, but if the device on the other end tries to send a response back and it has a particularly strong driver, and the arduino's resistance is too high, it could fry the arduino handily.