No Business Case For HDTV?
I used sageTV until I decided to get a HD tuner (DVICO dual tuner, forget the model name) since I was connecting to a 42'' plasma. Despite beta support for DVB-T sageTV did not work with the card at all (not blaming them, but was frustrating) so I went for MCE which works flawlessly. I should probably have tried mythTV but linux bugs me (granted I haven't used it properly in years).
All in all MCE is prettier than sageTV, but not quite as functional (no wildcard favourities is about the only thing missing really). More expensive too, unless you are building from scratch and need to factor in windows+sageTV, then MCE is probably equivalent.