I suppose linuxmce works well, if you have absolutely 100% the same hardware setup to the developers. After few days of attempting to download the mythical 5 click DVD (which doesn't exist on any sites or reasonable torrents anymore) I followed the kubuntu + 2 CDs setup (which is one of the longest setups ever encountered, and if you updated kubuntu in the meantime linuxmce starts chucking out errors. After complete fresh reinstall It failed to find my linux supported saa7134 dvb-t card at all, completely ignored liRC supported ea65 remote and once I forced dvb-t card and modules to autoload properly it served me with diabolically ugly interface with huuuuuuge fonts sticking out of their GUI boxes, I guess they never bothered to check if it works in my resolution 1280x1024. Reading across network was too slow (card module under kubuntu not optimized?), wireless dongle never kicked in. In fact, standard gentoo setup (my freevo adventure) worked much better with all the devices (nothing exotic, all linux supported).
Overall the idea is great - thin clients in all rooms, etc, etc, but forcing linux to do things it was never designed for is still a bit like trying to propel shopping cart to 60mph in under 6 seconds to prove it can be method of locomotion.
Meanwhile open source Media Portal under windows is just pleasure to work with. But it doesn't have to jump through all the hoops mythtv must do in what effectively is pure server platform. Getting non Hauppauge DVB-T, regardless of support, to work properly in linux and mythtv can be such a chore, that at the end of the day you feel like you were trying to make dishwasher produce toasted bread. And then you add DVB-S as second card and that's where the real fun begins. Don't get me wrong, it can be done, but why would you - just use that XP COA, put Media Portal on it and you'll have it up and running in 1/10th of the time. If you need to script things on it just install cygwin.
Leave linux to do what it does best.
