I'm also interested in hearing how this works. I used SageTV way back and it was solid.
...Have you played around with it?
jeez, just realized who you are from TGB and AVS. Honestly, i'm not stalking you!!
I've been using the SageTV miniclient for TV for awhile, installing alpha versions and what have you.
It's very, very good now and could replace an HD300 (the old dedicated SageTV extender hardware) depending on your use case. Works brilliantly for me with live & recorded TV from a SiliconDust cable card tuner (provider is Comcast which only sets the DRM flag on premium channels like HBO). So the files are 480i/720p/1080i MPEG2 transport streams (TS). Comskip works too. I've also played h.264 content in an MKV container without issues.
What else do you want to know? Since SageTV was open sourced by Google, there's not anything stopping you from trying it. I'd recommend going to the Open Source subforum on Sage.tv for more info (& links to installers, guides, etc)
Wait.. How did you get portal and hl2 on there?