You had to get 2 cards one for each tuner card in the TiVO and they would constantly fail and had endless issues. I was a Cablevision (a New York cable company) technician at the time.
The parts that sucked about CableCard mostly sucked because a lot of cable companies wanted them to suck, but the suckage was not mandatory.
Even the built-in Windows Media Center gave me a better interface and tons of storage versus the junky old cable boxes for rent, but then they used confusion over the switch to broadcast digital to stop providing Clear QAM channels and move everyone over to digital encrypted cable boxes.
For a while I really wanted to buy one of those fancy Ceton cards that took a CableCard like a TiVo, but between the cost of the tuner card and the horror stories I read about getting $CableCo to support anything but a TiVo I just said screw it and stopped buying cable at all.