CRN has an article about the new Digital Cable-ready Vista Media Centers that are beginning to "trickle into the market". Part of the article talks about some of the issues with CableCard support in Windows, most of them around the issues with OEMs and certification.
It's important to note that most of the problems with CableCard are the fault of CableLabs, not Microsoft. The Media Center team had to jump through a million hoops just to get the support in Vista, and they're controlling the certification process. At this point, Microsoft is hoping that the Digital Cable Tuners really take off in the market, so that they have leverage against the cable conglomerates to deliver the features that customers (but not necessarily cable companies) want, which would include more OEMs.
I've been a DCT (formerly OCUR) beta tester for over a year now, and I can say that the benefits outweigh the current limitations. I'm hoping that in the future (hopefully in "Fiji"), our options for "fair use" of the recorded content will be expanded.