This update completely crashed my Windows 7 Home Premium partition - wiped out all Restore Points, as well as BSODing on normal boot and any safe mode boot. I went though the usual troubleshooting: Initially trying to revert to an earlier restore point via the Win 7 install DVD, only to find they were gone; doing Startup Repair once I found that I couldn't even boot into safe mode (it found no issues, which is always fun) and running chkdsk/sfc/etc.; posting BSOD minidumps to other forums for analysis, which essentially told me the same thing (remove Avast), which I was sort of able to do through another partition. The last thing I expected from an update I honestly don't recall choosing to install was a good ol' BSOD upon restart.
Thankfully I have a Win 8.1 partition, and the data from the Win 7 is accessible. However - really for my fiancee's convenience - I'd really love to be able at least boot into safe mode without freezing on "classpnp.sys" and then endlessly restarting when that mode is selected.
TL;DR - Bricked my computer, erased my restore points, and has genuinely been more difficult to resolve than some viruses/malware I've come across.