After reading all the other posts in this thread (well, most of them), I wanted to share my success story. I was pretty nervous about getting my cable cards installed into my Tivo HD, but I finally made the call and got my install scheduled. I made sure to mention to the person on the phone that I wanted M-Cards and although he didn't know what those were exactly, he said he'd put that on the order. The day of the install came (I was also getting Digital Voice added, so that meant swapping out my old cable modem with their new one) and I asked if he had S-Cards or M-Cards. Surprisingly, the installer didn't know what an M-Card was either, but wouldn't you know, he stopped by their warehouse (Comcast in my area contracts out their installs) and picked up *4* M-Cards. I was pretty pleased to see all of those. The installer said he's never done a Tivo setup before, just some cable-card ready TV's, so we got out the Tivo instructions and followed it... inserted the card, he called it in and had them hit the card. I did end up having to reboot my Tivo and because we hadn't finished swapping out my cable modem yet, running the guided setup had to be delayed until Internet was back online because once you start guided setup, apparently you can't exit out of it... even after restarting the Tivo it still bugs you to run the setup. And you apparently MUST have Internet or phone available during the setup so it can contact Tivo. With both my Internet *and* phone unavailable during the Digital Voice setup, we had to go finish that part, then come back and finish the setup, and 20 minutes later (ugh...) it finished. At that point, everything was groovy... channels were all online on both tuners, great signal, no problem. I was pleasantly surprised it went so well and I only wish I'd waited to re-run the guided setup until after I'd verified the cable-card was okay. But I made sure the installer stuck around until it was done just to make sure we didn't have a bad card or anything. By the way, he knew all about the problems of having cable modems and cable cards show up in the right order on the provider side of things and said that wouldn't be a problem, so the reports of problems with that have apparently filtered through and made it all the way down the line, no problems there. Oh, and after getting my new cable modem, my Internet speeds are SIGNIFICANTLY higher! My old one was one I purchased myself and was 3-4 years old and only supported DOCSIS 2.0 (maybe not even that, but I think it did)... the new one should support up to DOCSIS 3.0 and who knows, maybe Comcast in my area (Pierce County, Washington state) is using it. All I know is, I was getting speeds up to 20 Mbps down and 1 Mbps up, whereas previously I could maybe get 8 M down, 384 K up.