As of April 1st, cable companies are required to provide a Firewire-enabled cable box to anyone that asks, as per an FCC interpretation of Section 304 of the Telecommunications Act of 1996. What this means to you is that easy ripping and recording of HDTV streams is just a phone call to your cable company away—at least those streams that are unencrypted (broadcast stations are required to remain unencrypted, and while most premium channels are open now, too, they likely won't be for long). Not only can you record shows and watch them on your computer, but the Firewire port allows you to stream video back to your TV, making the cable box, if nothing else, an extremely easy way to get a high-quality signal back into your existing A/V setup.
MacOSXHints has a howto for Apple users with more information, but there's no reason that, with a little futzing here and there, users of any OS wouldn't be able to take advantage of this rare consumer advocacy from the FCC. Thanks, Dan!