One experience - some good some bad
I upgraded by desktop, and bleeding edge XUbuntu to 16.04 last week and it was fine. No problems at all. It just worked. Very happy.
So I upgraded the LTS server from 14.04 to 16.04.
There are various sites that say you need to update to 15.10 before you go to 16.04. That would seem to defeat the whole idea of LTS, so I ignored them.
Why did I want to upgrade? I wanted the support for LXD. Then I can partition the server workflow in to separate units that do Mail, HTTP, proxy, file server, media server, etc. More isolation, so that a fault in one does not impact on any others.
That could have gone better. First it nuked MySql, and said I had two versions running simultaneously. Loads of errors, including a reference to the fact that it could link to to DropBox. MySql? DropBox? No., I didn't get that one either. Official advice is to uninstall MySql, and all its components. That means uninstalling all the Postfix/courier/authDeamon stuff that also links to MySql.
Did that, and MySql came back sweet as you like.
Then reinstalled all the other gubbins, and mail went down. Hard down. Nothing. Nada Spent the next 6 hours trying to get mail back. First postfix came up pretty fine and could receive emails. But no mail client could connect. Sometime in, I realised that Thunderbird could not connect, but all the Mac's and iPhones could.
Then I got Thunderhead connected, can receive email, but can't send.
Then it all started working. I still have no idea what I did, or why it was broken in the first place, or how I fixed it. But it's working.
All apart from SquirrelMail. That has some very wierd TLS messages.
Message: Works well on Desktops. Take care on servers. But I can now stay on 16.04 for the next 4 years at least, and by then that server should be on the cloud anyway.
As for Systemd. it's fine. No issues. It works well. I don't see any degredation.