I ran the update last night to get 8.1, and had the BSOD this morning!
Turns out there is an issue with ESET and the update process.
I had to boot into recovery mode, and delete the firewall driver for ESET
system_service_exception (epfwwfp.sys)
Couldn't delete it from the command line, and the only way was to do it from safe mode.
I've uninstalled ESET, and will try installing it again tonight.