I updated this morning, following a superduper backup (thankfully) that does permission repair first. (MacBook Pro)

Download went fine, restart was slow, but came to login screen. Upon entering password, screen went to a gradient blue, then black with the message that there was a crash report in /Library/Logs/CrashReporter/SecurityAgent.crash.log, with a welcome to Darwin and prompt. Logging in with username and trying to continue or reboot gave error message of not being root. exit led back to the login screen, with same result after log on.

I was able to reboot and restore from the superduper backup. Unfortunately, I didn't look at the log file after booting from the backup. I'll wait for a fix before trying this again.