Just picked up the XFi modem. Works great for a couple hours then stops working. If I unplug it and plug it back in it starts up again and works for a few hours and same thing. It is hot to the touch as well.
Others who had that modem that were hot, exchanged them and the new ones weren't hot.
I have taken mine to my nearest Xfinity Store (15 miles) with just the modem and they gave me a new package that included all the wiring.