Cable card may be less than ideal in implementation as far as open source is concerned, but at least there, if you've got a cooperating cable provider, you can access much of that content in it's digital form, which is better than the previous options of analog capture.
So the question we need to ask is whether, from an open source perspective, this is actually going to improve things for us (I'm definitely skeptical on that), keep it about the same, or make it worse.
Didn't the cable companies finally kill CableCARD a year or two ago? Obviously, most will still give you one, but isn't the mandate dead? If so, it's only a matter of time before the remaining cooperation winds down.
Regardless, I think a robust market for consumer-owned set-top boxes is better for the DVR community than CableCARD ever was. Let's face it, no such mandate is going to be open source-friendly, so why not have a variety of commercial products that actually have to compete with one another for customers? In the end, open source projects such as mythTV and the wonderful (but in desperate need of an installer) Sage TV will benefit through the variety of work-arounds and hacks that develop. If nothing else, I can see someone developing a recording and playback peripheral device that "protects" the content while allowing scheduling and UI to be handled by software of the user's choice.