Win 8.1 users, be advised:
I just went to reboot my desktop running win 8.1 and it wanted to restart and update. Fine. Next thing I know it's stuck in "Updating 5 of 7" and "Don't turn computer off until done" and this was stuck on the screen for 15-20 minutes. I was getting worried it had crashed or was in a loop or something, but the HD light seemed to say otherwise so I waited. Then it FINALLY moved on, restarted, hung on the opening screen for about 5 minutes (which is a ridiculous long time), then restarted again, and finally gave me the sign on screen. Entire process was about 25 minutes.