We just got word that Comcast is finally upgrading the DVRs here in Washington. We've been stuck with old buggy firmware which means that my DVR crashes once or twice a week and screws up any recording that's over 2 hours long. It is the most hated piece of electronics in my house by a factor of 42. I keep it because I have no choice.
Vista Media Center promised to bring support for cable cards. The cable companies are really strict about the way they send you HD content so you have to buy a new PC which is certified with the cable card tuners, rent cable cards instead of cable boxes, and shell out a ton of money. It took a while, but systems are finally started to get certified and ship out the door.
Engadget got their lucky hands on some Dell machines that are about ready to ship. They had trouble installing the first one but that seems due only to a weak cable signal. The second one installed perfectly. I'm not sure I'm ready to spend ~$3000 for a dual tuner HD Media Center, but cut that price in half and I'll start to listen. If you've ever spent time with Vista Media Center, you can vouch for it's awesomeness.
They have put together a great FAQ that answers every one of the questions running through your head right now.