I got a DCT3416-I from Comcast last week. So far it has recorded nothing. It locks up when I try to record. It locks up when I try to watch TV. Today it locked up when I turned it on. Last night it said that it recorded two shows. They were there in my "Recorded Shows" folder. I went to watch one of them and the unit froze. When I say "Freeze" I mean the unit it locked up, remote commands do not work and pressing the buttons on the front don't help, and letting it sit for 10 minutes changes nothing, so the only way to reset it is to unplug it. Anyway, I unplugged it, reset it and waited for my DVR menu to repopulate. Then it told me that there were "No Recorded Shows" (even though I had seen the three there that it had supposedly recorded earlier in the evening. Anyway, just really frustrated at this point. Going to get a new unit this afternoon, hopefully it helps. And yes, there is enough airflow to the unit.
I wish Tivo worked with On-Demand because I do like that service.