Preface: I don't know anything about TV Tuners (yet). I also have never used Comcast HD, but I am a Comcast customer (no HDTV). So I'm looking at running MythTV on my yet-to-be-built new machine. I ...

I've used TiVo for 4 years. It is an older series 2 unit. It doesn't really have enough RAM for the latest firmware TiVo had pushed to it and it is really slow. I've used it with Comcast analog cable.