OK Linux nerds you win.

XBMC? MythTV? Linux Huludesktop app? What do you want to do that doesn't include a cable card?

OpenElec is a XBMC distro so I guess that choice is made. My Linux box is multi-use so I installed the full Ubuntu desktop then XBMC. Cablecards only work with WMC so for HD you're limited to component video capture from a digital cable/sat box, OTA from antenna, or QAM from cable. The PVR feature in XBMC works only as a front end to other software like MythTV or TVHeadend and it's still not fully functional with features like timeshifting (pause,ff,rr etc) spotty at best. It does, however, work pretty good for scheduling/viewing recordings and is great for extensive movie and TV series collections.

I personally use MythTV with the Mythbox addon for XBMC rather than the XBMC PVR version. For live tv viewing I use an ATSC HDhomerun with a XBMC TV Guide addon mostly for sports but again there's no real timeshifting function so you have to be quick if you drink a lot of beer. You can, if needed, use XBMC to open a program so that you can have a menu item for MythTV or other PVR app and have quick access to a full featured PVR.

I think that if recording and viewing TV was high on my priority list I'd use WMC but since my cable company only offers 4:3 SD feeds I've found other ways to satisfy my viewing requirements.

Mythbox or MythTV, can do HD Homerun Prime, and get all but the copy-once channels.. which depending on your cable provider, could be almost all (Comcast except for Premium/PayPerView) or none (FIOS?).

I've setup a MythTV server backend, with several OpenElec eden beta2, mythbox, and HDHomerun duals for OTA.. and we are turning off cable in July!