I had a firewire PC and laptop connected to one of the fancy cable boxes. I never really got the firewire to work reliably with the cable box provided by my cable company.
Note that encryption was on cable/satellite only.
OTA broadcast channels CANNOT be, weren't and aren't encrypted. That's a requirement of being to able to transmit in the US. However, that doesn't mean that some of the cable providers didn't mess up and sometimes "forgot" to enable the broadcast flag on broadcast channels relayed over their cable network.
Cable card was a real pain as well, but worked well enough with my silicondust ethernet enabled tuner to record even pay channels like HBO.
I've since moved to a OTA silicondust tuner after ditching cable and it's NEVER had any problems sending OTA channels to be recorded by my media server unencrypted.