I finally threw in the towel on Windows Media Center's PVR and am now using an inferior cable company PVR instead. There was really only one channel that I watched regularly and the cable company was moving it to a digital channel not within reach of the analog cable dual tuner I was using in my Media Center system.
The new box isn't nearly as good as what was provided by Media Center and it's hard to believe some of the problems that exist on the cable company PVR.
Besides having a user interface that looks like it was generated by a Commodore 64, it has some other problems.
It will, for example, duplicate episodes in series recordings when they air multiple times on one day. This is a problem with guide data that doesn't distinguish new from repeat episodes for some stations, no doubt. But Media Center had a solution for it (to set an "around time" so that episodes are only recorded in the vicinity of a certain time each day -- this allows for minor schedule shifts as well as avoiding duplicates).
It will also -- and this is really hard to believe -- not let you customize your TV listings to only show the channels you can actually get. Since I'm on basic cable, I have to scroll through pages of listings for channels that I mostly can't get, with no indication of what I can actually watch. Media Center let you configure the guide by putting a checkmark next to the channels you want to see in the guide.
It will also not turn itself off if it is turned on when a recording starts. If it is turned off when a recording starts, it will turn itself off afterwards. If it's not, it won't.
I was also not looking forward to a few dollars extra on my power bill by adding the power load of a PVR that always keeps its drive spinning whether it's being used or not, but this has been somewhat mitigated by the surprising fact that removing the TV tuner card from my Media Center cut the power consumption of the system by 12 watts (which is worth about $1/month).
I am still using the Media Center for music and videos. I played with a WDTV Live to see if it could fill that gap and allow me to cut the cord between the Media Center and my TV but, while it was very good, it wasn't quite good enough. Most importantly, it lacked a skip back / skip forward feature for videos, which is a feature I use quite often. Users have been requesting it for awhile now, it is not difficult to implement, and I find it very useful... so, even though I am someone who hardly ever returns anything, I did return it to where I bought it from.
Media Center failed to make the transition to digital cable support gracefully, more because lack of industry co-operation than anything to do with Microsoft's own efforts. I have a feeling that the industry will regret their decision not to co-operate because if Microsoft is serious about pursuing this market then they will have to develop a system that bypasses the cable and satellite TV services completely, and I have a feeling that they or someone else will get there eventually.