Missed points I've caught so far on SageTV:
SageTV runs on Windows, Linux or Mac.
I currently have 4 QAM (1 HDHomerun and 1 HVR-2250, with 2 tuners each) tuners on my system, and they work fine. The HDHR is MUCH easier to set up than the 2250. My currently system has 5 tuners: HDHR, 2250, and a WinTV-HD PVR. Never had a bit of trouble, other then when I mess with it. Been using SageTV for about 5 years, and I'm currently supporting 3 recording systems (mine, my dad's (he's 76) and my cousins)
SageTV can also record ATSC (over the air HD)
SageTV (on a Windoze box) and it's extender will play almost any file format you can throw at it.
It's being continuously updated, and if you have a problem that is in there software (not driver or system) you get a direct connection to the devs. About the only problem I've heard, is that sending them a file (like a section of a HD file) can sometimes be a pain, but that's mainly the lack of file editors, and email limits! Oh, and they have a great and active forums group, that can help with the little bumps.