Feeling well again.
Today (Tuesday), I explored more of Comcast's digital cable with the HD-3000. I found a 1920x1080 stream of UPN! It was hiding away on channel 107. This is very interesting, because the channel simply isn't available from the real set top box, or even visible in Yahoo's TV listings. I should probably find some kind of forum to ask about this stuff.
I also mapped more than 50 regular cable channels available in digital format. Annoyingly, I haven't found SpikeTV yet. MythTV spends over 4 hours every day on that channel because of Star Trek, and it would be nice not to have to waste CPU on it :P
Other stuff I've found: the music "channels" are crammed into a lot of the upper QAM channels starting at pid 21. I think that On Demand uses a bunch of channels in the 80s to stream the programmes. Either that or Comcast just likes to have lots of different versions of somewhat-scrambled Shrek on at the same time. I also found a great channel that has the video in the "little boxes" that annoys you in the On Demand menu system, on channel 105.11. See, the set top box doesn't actually scale anything. It just composites one of these small windows :)