I've had two Series 3 Tivo's with single-stream cards for months now, and they both work like a charm. No channel dropouts, black screens or spontaneous reboots at all. So over the weekend I got a Tivo HD for the guest bedroom. Yesterday Cox (Litchfield Park, AZ) came and installed a Mcard (after trying to install two single-streams, but the first one got hung up on a firmware upgrade that never completed). Got it working, went thru guided setup. All seemed to be fine. But then i went into my channel list to de-select all the channels that i don't need showing up in the guide (sorry, spanish golf channel!). When i clicked "Done" to return to live tv, there was the black screen. No channels. I clicked on the Tivo button, and there was black behind the Tivo menu (instead of the usual animated, colored background). Did a soft reboot, and all worked fine after. Anyway, gonna give it a few days of trial and error. But add me to the list of those having issues somewhere between my Tivo HD and the cable card.