*TL;DR*: YMMV, but upgrading worked/is working great for me
I suspect like many Ubuntu 10.04 LTS Server admins out there, I've avoided
upgrading any 10.04 servers I look after to 12.04 because it's always good
to give a new LTS some time to bed in. Well, today I let my VPS 10.04
upgrade itself to 12.04, and it all went swimmingly (from what I can tell).
My VPS doesn't do much (Lighttpd, PHP5, Percona MySQL, PureFTPD and
Wordpress, and that's pretty-much it...) so the upgrade didn't take too
long, and I left all my configuration files as I have them set up (my SSH
is Monkeysphered, as an example), but all the stuff I had before the
upgrade I still have after, and it all works still.
I'm not about to advocate widespread upgrading just yet (I have three
servers at work running 10.04 LTS, and I'd only be prepared to upgrade one
of them right now...), but it's looking like 12.04 is almost ready for
full-time server use.
Kind regards
Murray Crane