Comcast sucks. At least in my area it does, south Jersey. I had an old US Robotics/3Com Tailfin modem on another service, optonline, in another state for three years and did not have one problem with it. I move to south Jersey and sign up with Comcrap and all of a sudden after about six months I started getting random disconnects and I had to reset the modem almost everyday. I had techs come out on several different occasions and replace my lines and my splitters. By the way none of these guys checked the levels at the ground block or at the tap.
Anyway, I still had problems. Finally the last tech said it was my modem, it supposedly and mysteriously decided to break all of a sudden I guess after three + years of no problems, yeah right. I hate renting anything so I went out and bought a Motorola SB5100 last year and figured i'd give a new modem a shot. Well about 6-8 months after I bought the new modem, guess what? Random disconnects and reboots. Wow, I guess yet another modem mysteriously broke after hooking it up to Comcast. So here we go again with the numerous tech calls and dealing with pompous Comcast customer service reps. The best was when one person told me I had to call immediately after every disconnect to get credit for the outage. I told her that would basically be a full time job on my end. Maybe they could install a red hotline(like the batphone) in my house to make things easier.
So again techs came out but couldn't do much this time because everything had been replaced already, including the drop going to my house. One guy told me, it's your modem. I said really? That makes two modems that when hooked up to your service suddenly break. Finally the last tech who came took readings at the head in and at the tap, and he said there was alot of line noise at the both spots. Even though the modem logs had good readings he said the tap signals were out of wack. He told me it was a system problem. Oh my Lord really? No sh*t. They had a line crew come out and readjusted the amplifier on my street and they replaced some stuff at one of the hubs. That was two weeks ago. The modem reboots stopped and so did the disconnects. Although today and yesterday I had three quick disconnects that didn't require a reboot. But that seems on par for whenever it rains in South Jersey, I noticed whenever it rains around here, the service get's flakey.
In a nutshell, it seems Comcast's quick answer is always it's your modem. BS. It's their service. Almost every problem I ever read about the sb5100 on any forum is when it involves Comcast.
By the way I had a person down the street from me who was renting a sb5100 from them, he went through the same crap with changing modems and still having problems. His problems also stopped when the line crew came out fixed the amplifier and the hub.