I thought my install of 14.04 was pretty standard, and it turns out I was wrong. Nothing went so bad that I had to nuke it from orbit, but it's been a couple of hours of repair work spread over a couple of days. 

Firstly, immediately after the update (and restart) systemd hosed pid 1 so the server wouldn't easily restart - I began to suspect something was up when systemctl wasn't controlling services, but service <blah> restart (et al) was still working so things didn't twig immediately. This only really came to light when I tried to restart the server after restoring everything else (see below) and that wasn't having it. Google came to the rescue, there's a way to forcibly reboot using systemctl even when pid 1 is hosed, and what was basically restart #2 got things happy again.

Not everything PHP 5 was automatically upgraded to PHP 7.0 (didn't have that much extra over -common, but enough that my website was down for 15 minutes or so). I had been tracking Nginx HEAD via their PPA, so it was a (very) minor downgrade to track the Ubuntu version (to avoid future problems, hopefully). The fly in the ointment turned out to be mysql; I had been using percona 5.6 (via PPA), but knew I wanted to track "stock" 5.7 (which the do--update did for me), but it zapped the config back to defaults, causing me two days to wondering why Codeguard couldn't back up my database - turns out that the default config only listens on 127.0.0.1 now... You learn as you go in my world.

Otherwise, a nice enough experience, and I'm loving the speed of PHP 7.0.