I got my TV tuner card moved over to Athena, the Linux box yesterday.  So today, I installed MythTV on it; either because I was bored, high or both.  It's actually pretty cool, although there were a couple of drawbacks for me.  The first is that Athena only has an Athlon 550 processor, so it's not too fast.  The second and bigger one though is that I don't have cable tv right now and don't know where my antenna is to use regular tv.  I might look for it later and try that out.  But for anyone looking for a PVR box who doesn't mind using Linux, I would recommend it.