I've been running MythTV for several months now, ever since my venerable DirecTV TiVO died a grisly death earlier this year. So far I'm loving it. It's reliable, stable, and records good quality video.
I am running MythTV on two separate machines. My Myth backend (the machine that actually contains the video capture card and does all the recording) is on an old P4 2.something GHz running Mythbuntu 9.04 Jaunty. Plenty fast enough for the single standard def capture card I record my DirecTV from. Unfortunately it's rather pokey when it comes to transcoding video. Since this machine is just a backend (i.e. it only does the recording, I don't actually watch TV on it), it runs headless (no monitor, keyboard, mouse). I use my Macs as the MythTV frontend, thanks to the excellent Mac OS X port of the MythTV mythfrontend software.
Like I mentioned before, my Myth backend (the Pentium 4 machine) is a bit on the slow side, and thus isn't good for transcoding video. However, my main desktop machine, an 8-core Intel Mac Pro, should have plenty of power for transcoding.
Is there any way I can run the transcoding tools, and have them fetch the data from my backend over the network? I normally use nuvexport to create iPod/Apple TV compatible H.264 video files.