I have much the same problems as sydyen, only using Time Warner Cable.
I broke down and tried their help desk via the web, explaining that I was digital/HDTV ready, and that my non-TWC DVRs/DVD recorders, and TV were losing digital channels. The first response was the basic "get ready for DTV" information. Well, since I am already ready for DTV, I responded that they hadn't answered my questions on why I was losing channels. I added a new question about whether they were forcing everyone to switch to their set-top boxes/DVRs except for local channels. Their second response was they were sorry they hadn't answered my questions and were elevating the problem. The final response was they were willing to send a technician to check my TWC DVRs to find out why I was losing channels. They just would not understand that my TWC DVRs were okay and that I was losing channels from my other equipment. They refused to answer my other question about forcing us to use their equipment.
Anyway, its getting to where I have to re-scan at least once a week, sometimes more. Even then, I can scan in the morning and a channel will be gone at night when I try to record. Now, they are creating new problems. For the CW, I get picture and sometimes no sound on digital station 112.1 on my DVR/DVD recorder and 112-13 on my TV (I guess the analog equivalent) and sound only on the supposedly HD station 104.10. Of course, the reception on 104.10 changes throughout the day. Sometimes it's both sound and picture, sometimes it's sound, sometimes it's nothing. Samething also happens on the HD version of NBC.
It seems like they can't keep the signal constant. Of course, that has always been a problem, even before DTV. One repairman would set the neighborhood signal strength one way to help out one customer and it would screw up everybody else. Then another repairmen would set it differently. And then there is always the ambient temperature factor that screws with the signal (dies in very cold morning's, but comes alive as the sun heats things up again).
By the way, I'm a newbie posting. Have been reading for several months and own several of both the 2160 and 3575/3576. Love this thread.
Am very interested in the hard drive upgrades to gain more recording time. I looked at HTPC thru their thread, but got overwhelmed with all the component choices/combinations. Whew! May still give HTPC a go if nothing like these boxes come out in the near future.