FWIW, I highly recommend going the Linux/MythTV route. Without starting a flamewar here, I found Media Centre to be very restrictive in what you can do with it. MediaPortal is quite nice and a bit more open to user customisation. For full tinkerability however, you can't go past Myth. Once set up (and that is the fiddly bit) it's very, very smooth and 'just works'. Emphasis is on the 'once set up' bit though. If you don't like fiddling with MySQL etc, you may be better to stick with the Windows-based options I've mentioned.
I would like to use Linux but unfortunately it does not support blu-ray :-(
This is what I get with windows/mediaportal:
1. EPG from the DVB-T signal using EPGCollector into XMLTV plugin
2. Record 2+ programs simultaneously on dual tuner
3. One button play 20 random songs from the music collection, up-mixed to 5.1
4. Skip forward/back n seconds/minutes, pause etc
5. blu-ray playback with downsampled hd audio
6. Make full use of graphics HW acceleration of h.264 decode
How does Myth compare? Linux would be nice but the pay-for-view digital media seems not so well supported.