arusr:
How are you planning to interface the RPi to the Arduino? I've seen a couple examples of how it can be done, but I've had trouble implementing it myself.
Well, I was presuming it to be dead easy - the Arduino plugs into a USB port just as it does on a PC/ laptop. I think. You avoid worrying about protection and level translation on the Pi hardware interface, though there are some nice buffer projects around.
You need a powered hub with a 2(+) amp power supply; arguably you can plug the Pi power itself into the hub; you lose one port doing so but you still have a total of four (or more).