Has FileVault crashed? I've just enabled FileVault 2 on my mid-2012 MacBook Air and am worried it has crashed. 

I've entered all the details and clicked "Restart" and now have a greyed out System Preference pane with a spinner. 

If I try and manually restart from the Apple menu I'm told that System Preferences are stopping a restart. 

How long should this stage take? Is it safe to hit the power button? I know the encryption occurs after a restart.
Well after no action after an hour I restarted and was presented with a non-bootable SSD.

Luckily the task immediately previous to enabling FileVault was to run a backup so that was restored overnight...