For anyone that may get the wrong impression, SageTV *does not* support the Ceton Cablecard tuner. The closest approximation for Sage is an HD PVR 1212 hooked up with a cable/sat box (regular box, doesn't need to be a DVR box.)
Personally, I agree with the notion put forth by Somewhatlost. Dump cable, and fill your watching habits with other means. Assuming you haven't been watching exceedingly large sums of content for the last couple years, it's highly likely that you can find a backlog of TV series available at Netflix (either On Demand or in disc form) that will help you fill in the void that may be caused when you dump cable and lose a couple of cable shows (until they come out on disc less than a year later.)
Although it is an admittedly grey activity, a person can bump their Netflix plan up to 3 discs at a time for a month or two and fill up a large buffer worth of TV series or movies quickly by ripping and returning them. Then watching and deleting at their leisure. Add OTA, Netflix On Demand, free hulu and the ocasional Amazon VOD and you get a lot of content.
The above works out well if you tend to watch normal levels of TV. If you're parking it on the couch for vast stretches of time and usually consume 4 or more hours of content a day, day in and day out, you'll probably run out of content in short order. In that case, the endless feedbag of mindless cable/sat is probably the best option for a person.