Same here. If someone is watching something in the living room (HD box) and in another room (non box), the non boxed program is a good bit ahead of it which is annoying as fuck hearing an "echo".
Its because the box has to process it, when its just coax to tv there is no processing involved.
I agree, I fucking hate comcast. But I had FiOS for a few weeks too and its not much better and it IS more expensive/contract.
Like doug said, I do the same shit. Every time comcast tells me my promotional time has expired I call them up and threaten to quit, done it about 6 times now. Just call them and tell them to transfer you to cancellations and that you can't justify the price anymore, they'll lower it. I pay $80/mo. right now for internet/catv with a HD/DVR and another HD box for the bedroom.
My HD box in the living room is hooked up to a Pioneer Elite reciever via hdmi, then to a projector via hdmi, I have no problems with it displaying 4:3 content IN 4:3 and 16:9 in 16:9. SD TV looks HORRIBLE on a 105" screen, I can't even stand to watch SD programming anymore. That was the one thing about FIOS I liked, the SD looked MUCH better then Comcast's SD.