Just wanted to share my experiences getting the InfiniTV up and running. This is long but hopefully it's informative/entertaining.
For reference, I just built an HTPC with an i5-2500, Gigabyte GA-H67MA-UD2H-B3 mobo, 8 GB 1600 RAM, 64 GB SSD, and 2x 2TB drives. Basically, I used the Assassin guides and went for the high end version.
I installed the InfiniTV 4 PCIe version and called my cable provider (TWC in SW Ohio) for the CableCard and TA. The rep told me they could not mail these to me and had to set up an installation by one of their techs for $19.95. The first available installation date was 2 weeks from then. I know they are supposed to give these to me, but knowing how out of touch TWC is, I said "fine."
The day after, I tried chatting with a TWC rep online to see if I could get the CC/TA quicker and through the mail. They told me it was available at their retail store.
So, I drove 35 minutes to the nearest retail store, stood in line for about 30 minutes (it was a big rush for some reason), and was unsurprised to discover they were out of the CC/TA. I had the rep there look up other stores nearby to see if they had any in stock. There was another store about 40 minutes from there that had one CC and two TA's left. Knowing that I might need two TA's for this install, I asked them if they could hold them for me. The rep took my name and relayed the information via chat with the rep at the other store.
I drove 40 minutes to the other store to find out that they had given away the CC/TA and they only had the one TA left.

I asked if they could let me have the TA because I was really dubious of me ever getting a CC/2 TA's from them. They said no, so I just left. Before I left, though, I did look at the TA to check the model. It was a Cisco STA1520, and I did verify later to see if these were capable of tuning 4 streams. Honestly, I was not surprised by any of this. This is par for the course when it comes to TWC.
I opened a ticket with Ceton to see if they could intervene on my behalf. They promptly responded to my ticket and did talk to TWC to see if they could get me a CC/TA.
About a week later (2 days ago), I got a random call from a TWC rep apologizing to me and assuring me they would have someone come out and give me a CC/TA the very next day. I can only assume that Ceton must have gotten through to them because I have never received this amount of attention from TWC. So, a HUGE THANKS to Ceton!
They set up an appointment and about 30 minutes later, I got a call from the tech that was assigned to work with me. Now, this guy was fairly clueless about the whole InfiniTV installation, and it even took a fair amount of hand holding to get him to navigate to TWC's own pages regarding the InfiniTV. I also had to convince him that I would be installing it and not him because I didn't trust him coming to my house and messing with my HTPC especially since I was probably not going to be the one answering the door when he got there. Still, to his credit, he was very understanding and he agreed to let me be in charge and to ask him for any help I would need. He was also genuinely curious about this new product, so I was more than happy to show him how it worked.
He came to my house yesterday and I was able to meet him. He did bring the things I had asked for. It took a little bit of time to get the TA up and running. I didn't realize the TA would be that much of a hassle, and I am glad he was there for that. I am also glad he had a splitter and extra cables. We had some issues getting the CC recognized. Both of us couldn't figure out what was wrong even after we mutually agreed on the way to install it based on the pictures in the installation guide. Then, my wife unceremoniously took the card out, flipped it over, and bam! It worked!

The tech then paired up my CC/TA with my TWC account settings (we do have HBO and Showtime and both appeared to work as intended). The rest of the installation as far as getting the tuners set up with WMC was a breeze. Luckily, I didn't need a second TA. The next steps will be to see if it stays stable. I will eventually get an Xbox to see if I can extend the TV tuner and recorded shows over my network. While it took a couple of hours to get the CC/TA installed and running, I am more than happy with the service from this tech. Yes, he was clueless about the InfiniTV, but he was a very nice guy and very helpful as far as getting the TA/CC set up. On top of that, I hope I taught him a bit about what the InfiniTV is and maybe he can pass that knowledge onto other techs and/or apply it on his future encounters with the InfiniTV. By far, it was the best encounter with a TWC rep I have ever had.
As for the InfiniTV performance, I am very happy with it so far. Shows look just as good as before on my HD TV. Browsing through the WMC guide is a billion times better/faster than any cable/satellite STB I have ever used.
Finally, I will say that so far Ceton seems like they have good customer service. Also, if you can get a tech that is nice/helpful, that will make everything smoother.