I purchased an Xfinity Gateway Modem 9/1/14 and it arrived in what appeared to be new packaging with instructions. Got it up and running fine.
In March 2015, Comcast started billing for a rented gateway modem. After speaking to Comcast, they advised they do not sell their modem and only lease it. They advised that the modem I purchased was stolen and that I should return it to Dontleaseyourmodem.com. I don't know if this is true or not, but Comcast is going to continue charging for the rental, unless I purchase another compatible modem to use.