Hi, I strongly suspect that the USB connection can be used for other then MIDI, but I have not used the USB port at all and I am not sure of how to use it. I am mainley into music and video and haven't found a need for the USB port. I use the audio connectors and the MIDI connections from the IO Dock to connect into and out of my Tyros Keyboard.
I can say that the IO Dock does charge the I Pad3 and it is fantastic, cause it keeps the I Pad continually charged.