I've been able to use my Mighty Mouse, iPod nano, and powered USB stick all at the same time when plugged into the USB hub, which in turn is plugged into my new Apple keyboard. Good luck trying it out.
[robg adds: I can't confirm this one, though is seems strange that it would work without the USB hub's power cord plugged in. If anyone has the new keyboard and can test with one or more USB hubs, please post your results.]

