I'm playing with the RaspBMC build http://www.raspbmc.com/ and am experimenting with hooking it up to my MythTV server. I've found that due to licensing and CPU reqs the Pi won't play back the MythTV recordings (I'm in the UK, so they're MPEG2s), but if I substitute a recording file with a different format it will play fine, so I'm looking at transcoding the recordings after I record programmes (I will have to deal with live TV streaming later, but that's not so important to me, at the moment). I was wondering if anyone had already looked at this, and if so what they did and if they had any success?
In the meantime, I'll carry on playing, myself, and post back any progress I make on here.