The 4.2 iOS GM seed is out. CoreMIDI is coming to the masses. So I've updated my CoreMIDI example to show how to send MIDI out through the USB port. (I've had a lot of people ask me for this.)
Go to the GitHub project page and check out the update. It's a simple addition, but shows the simplest way of getting MIDI data out of your application and through CoreMIDI.
Interestingly, the later - and the GM - versions of iOS 4.2 are far less forgiving of attached USB control devices. Most of the devices I test with are rejected by the iPad because they draw too much power. These are devices with LEDs, but that are certainly within USB power specifications. That's quite a shame.
As ever, I welcome feedback about this example project. Let me know if you find it useful.