HDHomeRun is not a Happauge product. It's from SiliconDust. I have 100% signal coming off my 7db attenuation splitter port, no problem here at all, but I'm FiOS. The 3db port off the splitter goes to my Verizon router. SiliconDust does not have a USB device. If there was a CableCard USB device, it would be extremely bulky, as the M Stream CableCard is the form of the old PCCard/PCMCIA card.
The HDHomeRun Prime has 3 cable tuners within. I also have a two-tuner HDHomeRun non-CableCard tuner, which receives either ATSC antenna or unencrypted digital cable (ClearQAM). All 5 tuners are available within my Windows Media Center, and all can be recorded and/or watched simultaneously. I don't have to perform any manual "switch inputs" as you mention.
The limit of tuners on Windows 7 is four of each type, not two. So you can have 4 analog, 4 digital antenna, 4 ClearQAM, and 4 CableCard tuners at the same time. There's an application called TunerSalad ($5) that ups the limit to 12.
I have not had any issues with encryption, or HDHomeRun or PC lockups, and these are not new installations.
I stream TV to two dedicated HTPCs, my home office PC (which I'm on now and watching cable TV), and one iPad2.
Verizon charges me $3.99 per month to rent the CableCard, which I think is a rip-off, but it beats paying them for their DVRs and set-top boxes. The only real disadvantage is that a movie recorded on one HTPC cannot be viewed on another if the channel is marked as "do not copy". This is mostly true with the big movie channels only, such as Cinemax, Showtime and HBO. The regular channel recordings work just fine on any of the systems.
To make this relevant to my post, the reason the do not record channels will work on the PS3 and not many other systems out of the box is because they support the standard required to do so. I think it's another advantage for the PS3.