I have noticed lately that Comcast upgraded yet again, the Firmware on most HD DCT's.
They have also made most of the digital lineup NON-5C Encrypted, so you should be able to record any channel.
Something that may be different, is the Resolution they are sending the files at now(544x480), and used to be the full (720x480) for standard def. HD Channels should record at 720P and or 1080i.
I do capturing ALOT myself through firewire.