I had major problems with my Pi's power and using the USB ports. First it started to lose the ethernet connection, then it would just start shutting down and rebooting. I ditched the whole controller and bought myself a Cubietruck and could not be happier. It had built in wifi and so far so good running 20 gridseeds.
Thanks for the tip. The Cubieboard2 looks like a safer option. I would hate to buy several Raspberry Pi and discover that it doesn't work with two 13 port usb hubs.