The Linux version is still considered OEM, which means the vendor won't help you install it but there's enough of a community that you can get it up and running with little or no trouble. (Heck, even I've dumped a bunch of notes into the wiki.) It's not to say that there aren't snags. The lastest update to V6 caused MP3s to not play via the Media MVP box. Luckily, I found this short thread which described how to fix the problem (turns out it was a missing library).
In any case, I will recommend getting SageTV to anyone who has more than a passing familiarity with Linux. If you can install the Hauppauge PVR-250 and the IVTV firmware, you'll love SageTV. Another notable thing about SageTV is that, unlike other similar commercial products, it's user modifiable. Heck, the $70 (or so) that I paid for it more than covers the amount of time (months!) that I would have spent pounding on MythTV to get it into the same shape. It doesn't hurt that SageTV now has a Mac client either. (One more reason I'm looking at getting a MBP once I can afford it.)(Sometime this year, I think.)