OK, very very odd. So after updating I verified it was ON. Then I noticed it wasn't working. Now I go back and check the settings...

Notification OFF for each mail account. Notification style set to NONE for each mail account. Lock screen notification set to OFF for each account.

I think that explains it. But not how any of those things, let alone all of them, suddenly got set to OFF.

Here's some bad design and carelessness (lack of attention to detail):

Do No Disturb appears as its own item in Settings and then again in Notification Center. The first instance only lets you turn it ON/OFF but setup requires going into notification center. Too awkward.

When you have Do Not Disturb ON, either manually or via schedule, plugging the phone into power will still produce a vibration, turn the screen on and play a sound. WTF. Sorry, it should vibrate and nothing else. When you're plugging the device in to power with someone sleeping only a few feet away, it's not very cool to chime a loud sound and light up the screen.