As you found, the b2 update eliminated TivoHD-related pixelization issues with Motorola CableCards.
The update cannot eliminate pixelization related to source encoding (i.e. overcompression), which is what you still see with the cable company's own STB / DVR. Nor does the update eliminate pixelization due to a poor signal, which can result from defective or split coax cabling, defective splitters, too many in-line splitters, or over-amplification.
If you are still seeing pixelization with FiOS (or another provider that uses Motorola CableCards) on new recordings made after the update was installed, then you need to schedule a service visit to have them adjust your signal levels. The tuner in the TivoHD is more sensitive than the tuner in the Motorola boxes. If your cable signal is too weak or too strong you will get constant pixelization with the TivoHD.
I have 2 Motorola S-Cards and 8.1.7b2 installed and I still get micro blocking and pixelization. The weird thing is the SD channels are the worst, to the point they are unwatchable.
In the case of FiOS, Verizon puts out a cable signal that is "20 db hot" from the ONT (the box on the outside of your home). You've probably seen this mentioned on their commercials. "Hot" refers to the signal strength. They output such a strong signal from the ONT so older cabling and multiple in-line splitters don't cause problems. However, as is, the signal is often too strong for the Tivo and pixelization can result.
Signal levels vary somewhat depending on the make and model of your ONT.
If you are using FiOS and see pixelization after the B2 update, then Verizon will need to come out and adjust your signal levels so they are more appropriate for the Tivo. They should swap out the splitter and try your setup with and without an attenuator. If you have another splitter lying around, you can also trying installing that in front of the TivoHD to see if that reduces the FiOS signal to a level the Tivo can handle.